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 the temporal correlation between frames, and intra-prediction, which utilizes the spatial correlation within a frame, and then perform orthogonal transform processing, loop filter processing, and entropy coding processing to output the resulting stream.

[0003] HEVC's intra prediction provides a total of 35 different 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, in 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 (for example, "512" for a 10-bit video image).

[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 extrapolating the nearest decoded reference pixel to the zeroth order.

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

[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 yet 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] Hereinafter, the above problem will be specifically described 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 Fig. 8(a), all reference pixels of CU#A1 (the upper left CU in the frame) have been decoded, as in the example of Fig. 7. Similarly, as shown in Fig. 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 top right CU in 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 is 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 reference pixel B1, which is located at the bottom of decoded reference pixels B1 to B3 located in CU#A3, is copied to undecoded reference pixel P3, which is located in the same column in a 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] In order to solve such problems, in intra prediction in which TU division is performed, a technique is known that aims to improve prediction accuracy by allowing freedom in the coding order for multiple TUs existing in 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 value coordinates," Information Processing Society of Japan SIGES 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 the transmission of a flag indicating which encoding process order to use on a CU-by-CU basis, which increases the amount of information to be transmitted. In addition, in order to select the best encoding process order from all the encoding process 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 and without increasing the calculation time on the encoding device side. [Means for solving the problem]

[0018] The first feature of the present invention is a decoding device configured to decode a block to be coded, which is obtained by dividing an original image in units of frames constituting a moving image, and includes a first prediction unit that generates a first predicted image by a first prediction process determined based on a prediction mode, a synthesis area determination unit that is configured to determine a synthesis area 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 area by a weighted average of the first predicted image and the second predicted image, and the predicted image synthesis unit determines a weight to be used for the weighted average based on whether or not a block adjacent to the block to be coded has been decoded. An encoding device according to one embodiment is an encoding device configured to divide an original image in units of frames constituting a moving image into blocks to be coded and code the blocks, and includes a synthesis area determination unit that is configured to determine a synthesis area in which a predicted image is generated from adjacent pixels that have not been decoded in the block to be coded based on an intra prediction mode, and an intra prediction unit that is configured to change a method of generating a predicted image for each area based on whether or not the block is included in the synthesis area.

[0019] A decoding device in one embodiment is configured to divide original images in units of frames that constitute a moving image 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] The gist of one embodiment of the present invention is that the program causes a computer to function as the encoding device described above.

[0021] The gist of one embodiment is that the program causes a computer to function as the above-described decoding device. Effect 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 and without increasing the calculation time on the encoding device side. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a functional block diagram of an encoding device 1 according to the first embodiment. [Diagram 2] FIG. 2 is a diagram showing an example of how a predicted image is generated in the first embodiment. [Diagram 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. [Diagram 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 PREFERRED EMBODIMENTS

[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 Fig. 1 to Fig. 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 upper sides of the CU to be encoded have already been decoded.

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

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

[0028] As shown in Figure 1, the encoding device 1 of 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 / quantization unit 15, an inverse orthogonal transform / 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 an optimal intra-prediction mode to be applied to a CU.

[0030] The synthesis region determination unit 12 is configured to determine a synthesis region 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 to cases where 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 addition, in the figures in this specification, the arrow indicating the direction of the intra prediction mode (prediction direction) points from the target pixel of intra prediction 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), the intra prediction unit 13 is configured to generate a predicted image using a pre-defined prediction method in areas included in the synthesis area X in CU#A2 (i.e., areas where 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 the 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 new flag indicating which area the synthesis area is from the encoding device 1 to the decoding device 3.

[0040] For example, as shown in Fig. 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 / quantization unit 15 is configured to perform an orthogonal transform process and a quantization process on the residual signal generated by the residual signal generation unit 14, and generate quantized transform coefficients.

[0043] The inverse orthogonal transform / 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 / 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 moving image into CUs and decode the divided images. Similarly to the encoding device 1 according to this embodiment, the decoding device 3 according to this embodiment is configured to divide a CU into a plurality of TUs.

[0048] As shown in Figure 4, the decoding device 3 of this embodiment includes an entropy decoding unit 31, a synthesis region determination unit 32, an intra prediction unit 33, an inverse quantization / 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 the 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 a signal that is encoded by dividing an original image in units of frames into CUs by the encoding device 1. Moreover, the flag information includes associated information such as a prediction mode.

[0050] The synthesis region determination unit 32 is configured to determine a synthesis region 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 output by the entropy decoding unit 31.

[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 a 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 FIG. 3(b), the intra prediction unit 33 is configured to generate a predicted image using the above-mentioned predefined prediction method in areas included in the synthesis area X in CU#A2 (i.e., areas where the reference pixels B2 to B4 have not yet been decoded).

[0056] The inverse quantization / 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 generating 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 an 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 an operation of generating a predicted image by the encoding device 1 according to the present embodiment will be described.

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

[0062] In step S102, the encoding device 1 determines a synthesis area X in which a predicted image is generated from adjacent 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 where the 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 predefined prediction method.

[0066] Secondly, with reference to FIG. 5, an example of an operation of generating a predicted image by the decoding device 3 according to the present 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 adjacent 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 in which the 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 reference pixels interpolated 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 a 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 a 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 FIG. 6, the 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 may be evaluated, for example, by a method of expressing the discontinuity 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 value.

[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 value.

[0080] 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 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 the decoding device 3 of this embodiment, it is possible to reduce discontinuity in boundary areas caused by changing the method of generating a predicted image for each area based on whether or not it is included in the synthesis area X, thereby improving the encoding performance.

[0083] (Third embodiment) Below, with reference to FIG. 6, the encoding device 1 and the 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 the 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 prediction image in an area included in the synthesis area X by taking a weighted average of a prediction image generated using a prediction method in conventional HEVC (a prediction image generated based on undecoded reference pixels filled in by copying) and a prediction image generated in the synthesis area X (a prediction 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 prediction image in an area included in the synthesis area X by taking a weighted average of a prediction image generated using a prediction method in conventional HEVC (a prediction image generated based on undecoded reference pixels filled in by copying) and a prediction image generated in the synthesis area X (a prediction image generated using the above-mentioned predefined prediction method) only when the above-mentioned specified condition is 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 a weighting factor used when calculating the weighted average.

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

[0088] In the example of Fig. 3(b), the reliability of the decoded reference pixels W1 to W4 is high, and the reliability of the reference pixels B1 to B4 generated by copying is low. In addition, when 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 depending on the distance from the boundary area between an area included in the synthesis area X and an 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 coefficient for a predicted image generated using a prediction method in conventional HEVC (a predicted image generated based on undecoded reference pixels filled in by copying) to be stronger near such boundary areas, and may calculate a weighting coefficient for a predicted image generated in the synthesis area X (a predicted image generated using the above-mentioned predefined prediction method) to be 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 description and drawings forming a part of the disclosure of such embodiment should not be understood as limiting 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 embodiment, 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 in a computer-readable medium. By using a computer-readable medium, such a program can be installed in a computer. Here, the computer-readable medium on which such a program is recorded may be a non-transient recording medium. The non-transient 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 implementing 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 section 14...Residual signal generation section 15...Orthogonal transformation and quantization section 16…Inverse quantization section / inverse orthogonal transformation section 17...Locally decoded image generation unit 18…Memory section 19...Entropy coding section 3...Decryption device 31...Entropy decoding unit 32...Synthesis area determination section 33…Intra prediction unit 34…Inverse quantization and inverse transformation section 35...Locally decoded image generation unit 36…Memory section

Claims

1. A decoding device configured to decode encoding target blocks obtained by dividing an original image in units of frames constituting 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 region determination unit configured to determine a synthesis region in the encoding target block; a second prediction unit that generates a second predicted image by a second 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 according to claim 1, wherein the predicted image synthesis unit determines a weight to be used for the weighted average for each pixel depending on a 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.

Images