Decoding device and program

Abstract

To improve prediction accuracy and encoding efficiency without increasing an amount of information to be transmitted by an encoding device and without increasing a computation time on the encoding device side.SOLUTION: An encoding device 1 comprises: a composite region determination unit 12 that on the basis of an intra-prediction mode, determines a composite region X, in which a prediction image is generated from adjacent pixels that are not decoded, in an encoding target block CU / TU; and an intra-prediction unit 13 for changing a method for generating a prediction image for each region on the basis of whether or not the region is included in the composite region X.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a decoding device and a program. [Background technology]

[0002] Video coding methods such as H.265 / HEVC (High Efficiency Video Coding) are configured to generate a residual signal by switching between two types of prediction: inter-prediction, which utilizes temporal correlation between frames, and intra-prediction, which utilizes spatial correlation within a frame, and then output the resulting stream by performing orthogonal transform processing, loop filter processing, and entropy coding processing.

[0003] HEVC provides 35 different intra prediction modes, including planar prediction, DC prediction, and directional prediction, and is configured to perform intra prediction using adjacent decoded reference pixels according to the mode determined by the encoder.

[0004] Here, in intra prediction, for CUs (Coding Units) that do not have adjacent decoded reference pixels, such as the CU located in the upper left corner of a frame, the reference pixels to be used when generating a predicted image are created by filling in a specified value ("512" for 10-bit video images).

[0005] In addition, in conventional HEVC, since the encoding process is performed in raster scan order from the top left, there are cases where the reference pixels have not been decoded. In such cases, a predicted image is generated using a value obtained by zero-order extrapolation of the nearest decoded reference pixel.

[0006] A CU is divided into multiple blocks (TUs: Transform Units) and orthogonal transform processing is performed on each CU. In HEVC, an intra prediction mode, which indicates the type of intra prediction to be applied, is common within a CU, and prediction is performed for multiple TUs using the same intra prediction mode.

[0007] In intra prediction, as shown in Figure 7, due to the encoding process in raster scan order, the reference pixel N located in the lower left or upper right of CU#X often has not been decoded.In such cases, if directional prediction is performed from the direction in which the undecoded reference pixel exists, the prediction accuracy decreases, resulting in a problem of reduced encoding efficiency.

[0008] These problems will be specifically described below with reference to Figures 8(a) to 8(d). Figure 8 shows an example of intra prediction in conventional HEVC.

[0009] In this example, as shown in Figure 8(a), all reference pixels of CU#A1 (the upper left CU in the frame) have been decoded, as in the example of Figure 7. Similarly, as shown in Figure 8(c), all reference pixels of CU#A3 (the lower left CU in the frame) have been decoded.

[0010] In contrast, as shown in Figure 8(b), reference pixels W1 to W3 located in CU#A1 have already been decoded, but reference pixels B1 to B4 located in CU#A3 have not been decoded, and therefore cannot be used as reference pixels when generating a predicted image for CU#A2 (the CU in the upper right corner of the frame).

[0011] For this reason, conventional HEVC stipulates that the value of the reference pixel W1 located at the bottom of the decoded reference pixels W1 to W3 located in CU#A1 be copied to the undecoded reference pixels B1 to B4 located in the same column in CU#A3, as shown in Figure 8(b).

[0012] Similarly, in conventional HEVC, as shown in Figure 8(d), it is specified that the value of the reference pixel B1 located at the bottom of the decoded reference pixels B1 to B3 located in CU#A3 is copied to the undecoded reference pixel P3 located in the same column in the CU below CU#A3.

[0013] Therefore, when directional prediction is performed from the bottom left to the top right, as in the example of Figure 8, many of the generated predicted images are composed of undecoded reference pixels filled with copies, resulting in a problem of reduced prediction accuracy and reduced coding efficiency.

[0014] To solve this problem, in intra prediction where TU division is performed, a technique is known that aims to improve prediction accuracy by allowing flexibility in the coding order for multiple TUs existing within a CU, such as raster scan order (e.g., Z-type), as well as U-type and X-type coding orders (see non-patent document 1). [Prior art documents] [Non-patent literature]

[0015] [Non-Patent Document 1] Mochizuki et al., "An adaptive intra prediction method based on mean coordinates," Information Processing Society of Japan Research Report, vol. 2012-AVM-77, no. Summary of the Invention [Problem to be solved by the invention]

[0016] However, the technology defined in the above-mentioned Non-Patent Document 1 requires transmitting a flag indicating which encoding processing order to use for each CU, which increases the amount of information to be transmitted. In addition, in order to select the best encoding processing order from all the encoding processing orders, the encoding device needs to try all combinations, which increases the calculation time on the encoding device side.

[0017] Therefore, the present invention has been made to solve the above-mentioned problems, and aims to provide an encoding device, a decoding device, and a program that can improve prediction accuracy and encoding efficiency without increasing the amount of information transmitted by the encoding device or increasing the calculation time on the encoding device side. [Means for solving the problem]

[0018]

[0010] A first aspect of the present invention is a decoding device configured to decode blocks to be coded, which are obtained by dividing an original image in units of frames constituting a video, the decoding device comprising: a first prediction unit that generates a first predicted image by a first prediction process determined based on a prediction mode; a synthesis region determination unit that determines a synthesis region corresponding to the block to be coded; a second prediction unit that generates a second predicted image by a second prediction process different from the first prediction process; and a predicted image synthesis unit that generates a predicted image included in the synthesis region by a weighted average of the first predicted image and the second predicted image, the predicted image synthesis unit determining a weight to be used for the weighted average based on whether blocks adjacent to the block to be coded have been decoded.

[0011] A coding device according to one embodiment is configured to divide an original image in units of frames constituting a video into blocks to be coded and code them, the coding device comprising: a synthesis region determination unit that determines a synthesis region in which a predicted image is generated from neighboring pixels within the block to be coded that have not yet been decoded based on an intra prediction mode; and an intra prediction unit that changes a method for generating a predicted image for each region based on whether the region is included in the synthesis region.

[0019] A decoding device according to one embodiment is configured to divide original images, each of which is made up of a frame, into blocks to be coded and decode them, and is equipped with a synthesis area determination unit configured to determine a synthesis area in which a predicted image is generated from adjacent pixels that have not yet been decoded within the block to be coded based on an intra prediction mode, and an intra prediction unit configured to change the method of generating the predicted image for each area based on whether or not it is included in the synthesis area.

[0020] A program according to an embodiment is a program for causing a computer to function as the encoding device described above.

[0021] A program according to one embodiment is a program for causing a computer to function as the above-described decoding device. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide an encoding device, a decoding device, and a program that can improve prediction accuracy and encoding efficiency without increasing the amount of information transmitted by the encoding device or increasing the calculation time on the encoding device side. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a functional block diagram of an encoding device 1 according to the first embodiment. [Figure 2] FIG. 2 is a diagram showing an example of how a predicted image is generated in the first embodiment. [Figure 3] FIG. 3 is a diagram showing an example of how a predicted image is generated in the first embodiment. [Figure 4] FIG. 4 is a functional block diagram of the decoding device 3 according to the first embodiment. [Figure 5] FIG. 5 is a flowchart showing the operations of the encoding device 1 and the decoding device 3 according to the first embodiment. [Figure 6] FIG. 6 is a diagram showing an example of how a predicted image is generated in the second embodiment. [Figure 7] FIG. 7 is a diagram showing an example of how a predicted image is generated in conventional HEVC. [Figure 8] FIG. 8 is a diagram showing an example of how a predicted image is generated in conventional HEVC. DETAILED DESCRIPTION OF THE INVENTION

[0024] (First embodiment) An encoding device 1 and a decoding device 3 according to a first embodiment of the present invention will be described below with reference to Figures 1 to 5. Here, the encoding device 1 and the decoding device 3 according to this embodiment are configured to support intra prediction in HEVC.

[0025] The encoding device 1 according to this embodiment is configured to divide an original image of each frame constituting a moving image into blocks to be encoded and encode the blocks. Note that in this embodiment, it is assumed that all pixels adjacent to the left and above the CU to be encoded have already been decoded.

[0026] Furthermore, the encoding device 1 according to this embodiment may be configured to divide a CU into a plurality of TUs. Therefore, in this embodiment, the encoding target block may be a CU or a TU. Hereinafter, this embodiment will be described taking as an example a case where a CU is used as the encoding target block.

[0027] Furthermore, in this embodiment, the case where the raster scan order (Z-type as shown in Figures 7 and 8) used in conventional HEVC is used as the coding order and decoding order of CUs is described as an example, but other coding orders and decoding orders such as U-type and X-type may also be used as such coding order and decoding order.

[0028] As shown in Figure 1, the encoding device 1 according to this embodiment includes an intra prediction mode determination unit 11, a synthesis region determination unit 12, an intra prediction unit 13, a residual signal generation unit 14, an orthogonal transform and quantization unit 15, an inverse orthogonal transform and inverse quantization unit 16, a local decoded image generation unit 17, a memory unit 18, and an entropy encoding unit 19.

[0029] The intra-prediction mode determination unit 11 is configured to determine the optimal intra-prediction mode to be applied to a CU.

[0030] The synthesis area determination unit 12 is configured to determine a synthesis area X in which a predicted image is generated from adjacent pixels that have not yet been decoded within a CU, based on the intra prediction mode determined by the intra prediction mode determination unit 11.

[0031] Specifically, as shown in FIG. 2, the synthesis area determination unit 12 may be configured to determine a synthesis area X in which a predicted image is generated from adjacent pixels B1 to B4 that have not yet been decoded within CU#A2 when the direction of the intra prediction mode determined by the intra prediction mode determination unit 11 is from the bottom left to the top right (i.e., when directional prediction is performed from the bottom left to the top right).

[0032] In addition, the present invention is also applicable when the direction of the intra prediction mode determined by the intra prediction mode determination unit 11 is from the top right to the bottom left (i.e., when directional prediction is performed from the top right to the bottom left), but below we will explain the case where the direction of the intra prediction mode determined by the intra prediction mode determination unit 11 is from the bottom left to the top right (i.e., when directional prediction is performed from the bottom left to the top right) as an example.

[0033] In the drawings in this specification, the arrow indicating the direction of the intra prediction mode (prediction direction) points from the pixel to be intra predicted to the reference pixel, as described in the HEVC standard (same below).

[0034] The intra prediction unit 13 is configured to change the method of generating a predicted image for each region based on whether or not the region is included in the synthesis region X determined by the synthesis region determination unit 12.

[0035] Specifically, as shown in Figure 3(a), in CU#A2, in an area Y that is not included in the synthesis area X (i.e., an area where reference pixels W1 to W3 have already been decoded), the intra prediction unit 13 is configured to generate a predicted image based on the decoded reference pixels W1 to W3 using the intra prediction mode determined by the intra prediction mode determination unit 11.

[0036] On the other hand, as shown in Figure 3(b), in CU#A2, the intra prediction unit 13 is configured to generate a predicted image using a pre-defined prediction method in the area included in the synthesis area X (i.e., the area where the reference pixels B2 to B4 have not yet been decoded).

[0037] Here, examples of the predefined prediction method include intra prediction such as DC prediction and planar prediction, as well as a prediction method that generates a predicted image by averaging values ​​of adjacent decoded reference pixels.

[0038] Furthermore, if the encoding device 1 and decoding device 3 have previously determined the prediction method, there is no need to transmit a new flag indicating the prediction method from the encoding device 1 to the decoding device 3, regardless of the prediction method used.

[0039] Furthermore, since the synthesis area determined by the synthesis area determination unit 12 can be uniquely determined based on the direction of the intra prediction mode and whether or not adjacent pixels have already been decoded, there is no need to transmit a flag indicating which area the new synthesis area is from the encoding device 1 to the decoding device 3.

[0040] 3(b), the intra prediction unit 13 may be configured to generate a predicted image by synthesizing pixels W3, D1, D2, and D4 using planar prediction at the position of pixel X1 in an area included in synthesis area X in CU#A2. Here, the value of pixel B4 is copied to pixel D4, and the value of pixel W1 is copied to pixel B4.

[0041] The residual signal generation unit 14 is configured to generate a residual signal based on the difference between the predicted image generated by the intra prediction unit 13 and the original image.

[0042] The orthogonal transform and quantization unit 15 is configured to perform orthogonal transform processing and quantization processing on the residual signal generated by the residual signal generation unit 14, and generate quantized transform coefficients.

[0043] The inverse orthogonal transform and inverse quantization unit 16 is configured to again perform inverse quantization processing and inverse orthogonal transform processing on the quantized transform coefficients generated by the orthogonal transform and quantization unit 15, thereby generating a quantized residual signal.

[0044] The local decoded image generation unit 17 is configured to generate a local decoded image by adding the predicted image generated by the intra prediction unit 13 to the quantized residual signal generated by the inverse orthogonal transform / inverse quantization unit 16.

[0045] The memory unit 18 is configured to hold the locally decoded image generated by the locally decoded image generating unit 17 so that it can be used as a reference image.

[0046] The entropy coding unit 19 is configured to perform entropy coding processing on flag information including the intra prediction mode determined by the intra prediction mode determination unit 11 and quantized transform coefficients, and output the result as a stream.

[0047] The decoding device 3 according to this embodiment is configured to divide original images of frames constituting a video into CUs and decode them. Similarly to the encoding device 1 according to this embodiment, the decoding device 3 according to this embodiment is configured to be able to divide a CU into a plurality of TUs.

[0048] As shown in Figure 4, the decoding device 3 according to this embodiment includes an entropy decoding unit 31, a synthesis region determination unit 32, an intra prediction unit 33, an inverse quantization and inverse transform unit 34, a local decoded image generation unit 35, and a memory unit 36.

[0049] The entropy decoding unit 31 is configured to decode transform coefficients, flag information, and the like from the stream output from the encoding device 1. Here, the transform coefficients are quantized transform coefficients obtained as signals encoded by the encoding device 1 after dividing an original image in units of frames into CUs. Furthermore, the flag information includes accompanying information such as a prediction mode.

[0050] The synthesis region determination unit 32 is configured to determine, based on the intra prediction mode output by the entropy decoding unit 31, a synthesis region X in which a predicted image is generated from adjacent pixels that have not yet been decoded within the CU.

[0051] Specifically, as shown in FIG. 2, the synthesis area determination unit 32 may be configured to determine a synthesis area X in which a predicted image is generated from adjacent pixels B1 to B4 that have not yet been decoded within CU#A2 when the direction of the intra prediction mode output by the entropy decoding unit 31 is from the bottom left to the top right (i.e., when directional prediction is performed from the bottom left to the top right).

[0052] The intra prediction unit 33 may be configured to generate a predicted image using the synthesis region X determined by the synthesis region determination unit 32 and the intra prediction mode output by the entropy decoding unit 31.

[0053] Specifically, similar to the intra prediction unit 13, the intra prediction unit 33 is configured to change the method of generating the predicted image for each region based on whether or not it is included in the synthesis region X determined by the synthesis region determination unit 12.

[0054] For example, as shown in Figure 3(a), in CU#A2, in an area Y that is not included in the synthesis area X (i.e., an area where reference pixels W1 to W3 have already been decoded), the intra prediction unit 33 is configured to generate a predicted image based on the decoded reference pixels W1 to W3 using the intra prediction mode output by the entropy decoding unit 31.

[0055] On the other hand, as shown in Figure 3(b), in CU#A2, the intra prediction unit 33 is configured to generate a predicted image using the above-mentioned pre-defined prediction method in the area included in the synthesis area X (i.e., the area where the reference pixels B2 to B4 have not yet been decoded).

[0056] The inverse quantization and inverse transform unit 34 is configured to generate a residual signal by performing inverse quantization processing and inverse transform processing (e.g., inverse orthogonal transform processing) on ​​the quantized transform coefficients output by the entropy decoding unit 31.

[0057] The local decoded image generation unit 35 is configured to generate a local decoded image by adding the predicted image generated by the intra prediction unit 33 and the residual signal generated by the inverse quantization and inverse transform unit 34.

[0058] The memory unit 36 ​​is configured to hold the locally decoded image generated by the locally decoded image generation unit 35 so that it can be used as a reference image for intra prediction and inter prediction.

[0059] FIG. 5 shows a flowchart for explaining an example of the operation of generating a predicted image by the encoding device 1 and the decoding device 3 according to this embodiment.

[0060] First, with reference to FIG. 5, an example of the operation of generating a predicted image by the encoding device 1 according to this embodiment will be described.

[0061] As shown in FIG. 5, in step S101, the encoding device 1 determines the optimal intra prediction mode to be applied to the CU.

[0062] In step S102, the encoding device 1 determines a synthesis area X in which a predicted image is generated from neighboring pixels that have not yet been decoded within the CU, based on the intra prediction mode determined in step S101.

[0063] In step S103, the encoding device 1 determines whether or not the area in the CU for which a predicted image is to be generated is included in the synthesis area. If "No," the operation proceeds to step S104, and if "Yes," the operation proceeds to step S105.

[0064] In step S104, the encoding device 1 generates a predicted image based on the decoded reference pixels, using the intra prediction mode determined in step S101.

[0065] In step S105, the encoding device 1 generates a predicted image using the above-mentioned predetermined prediction method.

[0066] Secondly, with reference to FIG. 5, an example of the operation of generating a predicted image by the decoding device 3 according to this embodiment will be described.

[0067] As shown in FIG. 5, in step S101, the decoding device 3 determines the intra prediction mode based on information obtained by the entropy decoding process.

[0068] In step S102, the decoding device 3 determines a synthesis area X in which a predicted image is generated from neighboring pixels that have not yet been decoded within the CU, based on the intra prediction mode determined in step S101.

[0069] In step S103, the decoding device 3 determines whether or not the area in the CU for which a predicted image is to be generated is included in the synthesis area. If "No," the operation proceeds to step S104, and if "Yes," the operation proceeds to step S105.

[0070] In step S104, the decoding device 3 generates a predicted image based on the decoded reference pixels, using the intra prediction mode determined in step S101.

[0071] In step S105, the decoding device 3 generates a predicted image using the above-mentioned predetermined prediction method.

[0072] According to the encoding device 1 and decoding device 3 of this embodiment, when an undecoded pixel is included in the reference destination of the direction (prediction direction) of the intra prediction mode, a new predicted image is generated by combining a predicted image generated using interpolated reference pixels by copying adjacent decoded reference pixels with a predicted image generated using a predefined prediction method, thereby suppressing a decrease in prediction accuracy.

[0073] (Second embodiment) Hereinafter, with reference to FIG. 6, the encoding device 1 and the decoding device 3 according to the second embodiment of the present invention will be described, focusing on the differences from the encoding device 1 and the decoding device 3 according to the first embodiment described above.

[0074] In the encoding device 1 according to this embodiment, the intra prediction unit 13 is configured to apply a smoothing filter to the predicted image of a boundary area between an area included in the synthesis area X and an area Y not included in the synthesis area X when a predetermined condition is satisfied in the boundary area.

[0075] Similarly, in the decoding device 3 according to this embodiment, the intra prediction unit 33 is configured to apply a smoothing filter to the predicted image of a boundary area between an area included in the synthesis area X and an area Y not included in the synthesis area X when a predetermined condition is satisfied in the boundary area.

[0076] For example, in the example of Figure 6, such a boundary area corresponds to the area where pixels X1, X2, X3, and X4 in the area included in synthesis area X and pixels Y1, Y2, and Y3 in area Y not included in synthesis area X are located.

[0077] The predetermined condition is that the discontinuity in the boundary region is higher than a predetermined threshold. Here, the discontinuity can be evaluated, for example, by a method of expressing it as a linear combination of horizontal differences, vertical differences, diagonal differences, etc.

[0078] That is, the intra prediction unit 13 and the intra prediction unit 33 are configured to apply a smoothing filter to the predicted image of the boundary region when the evaluation value of the discontinuity in the boundary region is higher than a predetermined threshold.

[0079] For example, in the example of Figure 6, the intra prediction unit 13 and the intra prediction unit 33 are configured to apply a smoothing filter to the predicted image of the area in which pixels X1, X2, X3, and X4 in the area included in the synthesis area X and pixels Y1, Y2, and Y3 in the area Y not included in the synthesis area X are located when the evaluation value of the discontinuity in such a boundary area is higher than a predetermined threshold.

[0080] In the example of Figure 6, the intra prediction unit 13 and the intra prediction unit 33 are configured to also apply a smoothing filter to the predicted image of the area in which pixels X5, X6, and X7 are located within the area included in the synthesis area X.

[0081] Here, by sharing the above-mentioned predetermined threshold between the encoding device 1 and the decoding device 3, it becomes unnecessary to transmit a new flag from the encoding device 1 to the decoding device 3.

[0082] According to the encoding device 1 and decoding device 3 of this embodiment, it is possible to reduce discontinuity in boundary areas caused by changing the method of generating the predicted image of each area based on whether it is included in the synthesis area X, thereby improving encoding performance.

[0083] (Third embodiment) Below, with reference to Figure 6, the encoding device 1 and decoding device 3 according to the third embodiment of the present invention will be described, focusing on the differences from the encoding device 1 and decoding device 3 according to the first and second embodiments described above.

[0084] In the encoding device 1 and the decoding device 3 according to this embodiment, the intra prediction unit 13 and the intra prediction unit 33 are configured to generate a predicted image in an area included in the synthesis area X by taking a weighted average of a predicted image generated using a conventional HEVC prediction method (a predicted image generated based on undecoded reference pixels filled by copying) and a predicted image generated in the synthesis area X (a predicted image generated using the above-mentioned predefined prediction method).

[0085] In addition, in the encoding device 1 and the decoding device 3 according to this embodiment, the intra prediction unit 13 and the intra prediction unit 33 may be configured to generate a predicted image in an area included in the synthesis area X by taking a weighted average of a predicted image generated using a conventional HEVC prediction method (a predicted image generated based on undecoded reference pixels filled by copying) and a predicted image generated in the synthesis area X (a predicted image generated using the above-mentioned predefined prediction method) only when the above-mentioned specified conditions are satisfied.

[0086] In the encoding device 1 and the decoding device 3 according to this embodiment, the intra prediction unit 13 and the intra prediction unit 33 may be configured to calculate weighting factors used when calculating such a weighted average.

[0087] The intra prediction unit 13 and the intra prediction unit 33 may be configured to use a predetermined value as a weighting factor, or may be configured to calculate a weighting factor using the reliability of decoded reference pixels when generating a predicted image.

[0088] 3(b), the reliability of the decoded reference pixels W1 to W4 is high, while the reliability of the reference pixels B1 to B4 generated by copying is low. Furthermore, comparing the reliability of the reference pixel B1 with that of the reference pixel B4, the reliability of the reference pixel B4, which is closer to the copy source, is higher.

[0089] In addition, the intra prediction unit 13 and the intra prediction unit 33 may be configured to calculate such weighting coefficients according to the distance from the boundary area between the area included in the synthesis area X and the area Y not included in the synthesis area X.

[0090] For example, the intra prediction unit 13 and the intra prediction unit 33 may calculate a weighting factor so that the weighting factor of the predicted image generated using a conventional HEVC prediction method (a predicted image generated based on undecoded reference pixels filled by copying) is stronger near such boundary areas, and may calculate a weighting factor so that the weighting factor of the predicted image generated in the synthesis area X (a predicted image generated using the above-mentioned predefined prediction method) is stronger in areas away from such boundary areas.

[0091] (Other embodiments) As described above, the present invention has been described by the above-mentioned embodiment, but the descriptions and drawings forming part of the disclosure of such embodiment should not be understood to limit the present invention. From such disclosure, various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art.

[0092] Although not specifically mentioned in the above-described embodiments, a program may be provided that causes a computer to execute each process performed by the encoding device 1 and the decoding device 3. Such a program may be recorded on a computer-readable medium. Using the computer-readable medium, such a program can be installed on a computer. Here, the computer-readable medium on which such a 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.

[0093] Alternatively, a chip may be provided that is configured by a memory that stores a program for realizing at least some of the functions of the encoding device 1 and the decoding device 3 described above, and a processor that executes the program stored in the memory. [Explanation of symbols]

[0094] 1...Encoding device 11... Intra prediction mode determination unit 12...Synthesis area determination section 13...Intra prediction unit 14...Residual signal generation section 15...Orthogonal transformation and quantization section 16...Inverse quantization unit / inverse orthogonal transformation unit 17...Local decoded image generation unit 18...Memory section 19...Entropy coding unit 3...Decryption device 31...Entropy decoding unit 32...Synthesis area determination section 33...Intra prediction unit 34...Inverse quantization and inverse transform unit 35...Local decoded image generation unit 36...Memory section

Claims

1. 1. A decoding device configured to decode encoding target blocks obtained by dividing an original image in units of frames that constitute a moving image, comprising: a first prediction unit that generates a first predicted image by a first prediction process that is determined based on a prediction mode designated by flag information transmitted from an encoding side; a synthesis area determination unit configured to determine a synthesis area in the encoding target block; a second prediction unit that generates a second predicted image by an intra prediction process that is different from the first prediction process and is determined without transmission of new flag information other than the flag information transmitted from an encoding side; a predicted image synthesis unit that generates a predicted image included in the synthesis area by taking a weighted average of the first predicted image and the second predicted image, The decoding device is characterized in that the predicted image synthesis unit determines the weight to be used for the weighted average for each pixel depending on the position from a boundary area between the first predicted image and the second predicted image.

2. A program for causing a computer to function as the decoding device according to claim 1.

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