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 Art

[0002] In video coding methods represented by H.265 / HEVC (High Efficiency Video Coding), prediction is performed while switching between two types of prediction: inter prediction using temporal correlation between frames and intra prediction using spatial correlation within a frame to generate a residual signal, and then orthogonal transformation processing, loop filter processing, and entropy coding processing are performed to output the obtained stream.

[0003] In intra prediction in HEVC, a total of 35 modes such as Planar prediction, DC prediction, and direction prediction are prepared, and intra prediction is performed using adjacent decoded reference pixels according to the mode determined by the encoder.

[0004] Here, in intra prediction, for a CU (Coding Unit) located at the uppermost left in a frame or a CU without adjacent decoded reference pixels, a reference pixel used for generating a predicted image is created by a process of filling a prescribed value (e.g., "512" for a 10-bit video).

[0005] [[ID=2U]] Also, in conventional HEVC, since the encoding process is performed in raster scan order from the upper left, there may be cases where reference pixels are not decoded. In such cases, a predicted image is generated using a value obtained by linearly extrapolating the nearest decoded reference pixel.

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

[0007] In intra prediction, as shown in Figure 7, due to the encoding process based on the raster scan order, reference pixels N located in the lower left or upper right of CU#X are often not decoded. In such cases, performing direction prediction from the direction where the undecoded reference pixels exist reduces prediction accuracy and lowers encoding efficiency, which is a problem.

[0008] The following will explain these problems in detail using 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 of the reference pixels for CU#A1 (the top-left CU in the frame) are decoded, similar to the example in Figure 7. Similarly, as shown in Figure 8(c), all of the reference pixels for CU#A3 (the bottom-left CU in the frame) are decoded.

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

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

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

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

[0014] To address these issues, a technique has been developed to improve prediction accuracy in intra prediction where TU partitioning is performed by allowing flexibility in the coding order of multiple TUs within a CU, such as U-type or X-type coding in addition to the raster scan order (e.g., Z-type) (see Non-Patent Literature 1). [Prior art documents] [Non-patent literature]

[0015] [Non-Patent Document 1] Mochizuki et al., "Applicable Intra-Prediction Method Based on Mean Coordinates," Information Processing Society of Japan Research Report, vol. 2012-AVM-77, No. 12. [Overview of the project] [Problems that the invention aims to solve]

[0016] However, the technology described in Non-Patent Document 1 above has the problem that, because it is necessary to transmit a flag indicating which encoding order to use for each CU, the amount of information to be transmitted increases, and because the encoding device has to try all combinations to select which encoding order is best from all possible encoding orders, the computation time on the encoding device increases.

[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 without increasing the computation time on the encoding device side. [Means for solving the problem]

[0018] A first feature of the present invention is a decoding device configured to decode encoding target blocks obtained by dividing a frame-unit original image constituting a moving image, 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 configured to determine a synthesis region corresponding to the encoding target block; 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, wherein the predicted image synthesis unit determines the weights to be used in the weighted average based on whether or not blocks adjacent to the encoding target block have been decoded. An encoding device according to one embodiment is an encoding device configured to encode a frame-unit original image constituting a moving image by dividing it into encoding target blocks, comprising: a synthesis region determination unit configured to determine a synthesis region in which a predicted image is generated from adjacent pixels within the encoding target block that have not been decoded, based on an intra-prediction mode; and an intra-prediction unit configured to change the method of generating predicted images for each region based on whether or not it is included in the synthesis region.

[0019] A decoding device according to one embodiment is a decoding device configured to decode a frame-by-frame original image constituting a moving image by dividing it into encoding target blocks, and comprises a composite region determination unit configured to determine a composite region in which a predicted image is generated from adjacent pixels that have not yet been decoded within the encoding target block, based on an intra-prediction mode, and an intra-prediction unit configured to change the method of generating a predicted image for each region based on whether or not it is included in the composite region.

[0020] The program according to one embodiment is, in essence, a program that causes a computer to function as the encoding device described above.

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

Advantages 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. [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 a 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 a conventional HEVC. [Figure 8] FIG. 8 is a diagram showing an example of how a predicted image is generated in a conventional HEVC.

Modes for Carrying Out the Invention

[0024] (First Embodiment) The encoding device 1 and decoding device 3 according to the first embodiment of the present invention will be described below with reference to Figures 1 to 5. Here, the encoding device 1 and 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 the original image, which constitutes a moving image in frame units, into blocks to be encoded and encode them. 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 multiple TUs. Therefore, in this embodiment, the block to be encoded may be a CU or a TU. In the following description, this embodiment will be explained using the case in which a CU is used as the block to be encoded as an example.

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

[0028] As shown in Figure 1, the encoding device 1 according to this embodiment comprises 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 the optimal intra-prediction mode to apply to the CU.

[0030] The composite region determination unit 12 is configured to determine a composite region 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 by the intra-prediction mode determination unit 11.

[0031] Specifically, as shown in Figure 2, the composite region determination unit 12 may be configured to determine a composite region X in which a predicted image is generated from undecoded adjacent pixels B1 to B4 within CU#A2 when the direction of the intra-prediction mode determined by the intra-prediction mode determination unit 11 is from the lower left to the upper right (i.e., direction prediction is performed from the lower left to the upper right).

[0032] Furthermore, 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 upper right to the lower left (i.e., when direction prediction is performed from the upper right to the lower left). However, the following explanation will use the case where the direction of the intra-prediction mode determined by the intra-prediction mode determination unit 11 is from the lower left to the upper right (i.e., when direction prediction is performed from the lower left to the upper right) as an example.

[0033] In the diagrams of this specification, the arrow indicating the direction of the intra-prediction mode (prediction direction) shall point from the pixel targeted for intra-prediction to the reference pixel, as described in the HEVC standard (the same applies hereinafter).

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

[0035] Specifically, as shown in Figure 3(a), the intra-prediction unit 13 is configured to generate a predicted image based on the decoded reference pixels W1 to W3 in the region Y that is not included in the composite region X in CU#A2 (i.e., the region where the reference pixels W1 to W3 have been decoded), 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 in CU#A2 using a predetermined prediction method in the region included in the composite region X (i.e., the region where reference pixels B2 to B4 have not been decoded).

[0037] Here, the predetermined prediction method includes, for example, intra-prediction methods such as DC prediction and Planar prediction, as well as prediction methods that generate a predicted image by averaging the values ​​of adjacent decoded reference pixels.

[0038] Furthermore, if the coding device 1 and the decoding device 3 have predetermined such prediction methods, it is not necessary to transmit a new flag indicating such prediction method from the coding device 1 to the decoding device 3, regardless of which prediction method is used.

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

[0040] For example, as shown in Figure 3(b), the intra-prediction unit 13 may be configured to generate a predicted image by combining pixels W3, D1, D2, and D4 using Planar prediction at the location of pixel X1 within the region included in the synthesis region 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 from the difference between the predicted image generated by the intra-prediction unit 13 and the original image.

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

[0043] The inverse orthogonal transform / inverse quantization unit 16 is configured to apply inverse quantization and inverse orthogonal transform processing again to the quantized transformation 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 a 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 generation unit 17 so that it can be used as a reference image.

[0046] The entropy coding unit 19 is configured to apply entropy coding to flag information, including the intra-prediction mode determined by the intra-prediction mode determination unit 11, and quantized conversion coefficients, and output them as a stream.

[0047] Furthermore, the decoding device 3 according to this embodiment is configured to decode the original image, which is composed of frames, by dividing it into CUs. Also, similar to the encoding device 1 according to this embodiment, the decoding device 3 according to this embodiment is configured to divide the CU into a plurality of TUs.

[0048] As shown in Figure 4, the decoding device 3 according to this embodiment comprises 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 decoding image generation unit 35, and a memory unit 36.

[0049] The entropy decoding unit 31 is configured to decode conversion coefficients, flag information, etc., from the stream output from the encoding device 1. Here, the conversion coefficients are quantized conversion coefficients obtained as signals encoded by the encoding device 1 after dividing the original image on a frame-by-frame basis into CUs. The flag information includes accompanying information such as the prediction mode.

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

[0051] Specifically, as shown in Figure 2, the composite region determination unit 32 may be configured to determine a composite region X in which a predicted image is generated from undecoded adjacent pixels B1 to B4 within CU#A2 when the direction of the intra-prediction mode output by the entropy decoding unit 31 is from the lower left to the upper right (i.e., when direction prediction is performed from the lower left to the upper right).

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

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

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

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

[0056] The inverse quantization / inverse transformation unit 34 is configured to generate a residual signal by applying inverse quantization and inverse transformation (for example, inverse orthogonal transformation) to the quantized transformation 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 / inverse transform unit 34.

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

[0059] Figure 5 shows a flowchart illustrating an example of the operation by which the encoding device 1 and decoding device 3 according to this embodiment generate a predicted image.

[0060] Firstly, with reference to Figure 5, an example of the operation by which the encoding device 1 according to this embodiment generates a predicted image will be described.

[0061] As shown in Figure 5, in step S101, the encoding device 1 determines the optimal intra-prediction mode to apply to the CU.

[0062] In step S102, the encoding device 1 determines a composite region 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 the region for generating the predicted image within the CU is included in the synthesis region. If "No", the operation proceeds to step S104; 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 predetermined prediction method described above.

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

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

[0068] In step S102, the decoding device 3 determines a composite region 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 the region within the CU for generating the predicted image is included in the synthesis region. If "No", the operation proceeds to step S104; 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 predetermined prediction method described above.

[0072] According to the encoding device 1 and decoding device 3 of this embodiment, if the reference destination in the direction (prediction direction) of the intra prediction mode contains undecoded pixels, a new prediction image can be generated by combining a prediction image generated using interpolated reference pixels obtained by copying adjacent decoded reference pixels with a prediction image generated using a predetermined prediction method, thereby suppressing a decrease in prediction accuracy.

[0073] (Second embodiment) Hereinafter, with reference to Figure 6, the encoding device 1 and 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 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 region between a region included in the composite region X and a region Y not included in the composite region X, when predetermined conditions are met in such a boundary region.

[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 the boundary region between the region included in the composite region X and the region Y not included in the composite region X, when predetermined conditions are met.

[0076] For example, in the example shown in Figure 6, such boundary regions include the areas where pixels X1, X2, X3, and X4 are located within the area included in composite region X, and pixels Y1, Y2, and Y3 are located within region Y, which is not included in composite region X.

[0077] Furthermore, a predetermined condition is that the discontinuity in the boundary region is higher than a predetermined threshold. Here, one way to evaluate the discontinuity is to represent it as a linear combination of differences in the horizontal direction, vertical direction, or diagonal direction, for example.

[0078] In other words, 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 if the evaluation value of the discontinuity in the boundary region is higher than a predetermined threshold.

[0079] For example, in the example in 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 region where pixels X1, X2, X3, and X4 in the region included in the composite region X and pixels Y1, Y2, and Y3 in the region Y not included in the composite region X are located, if the evaluation value of the discontinuity in the boundary region is higher than a predetermined threshold.

[0080] In the example shown in 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 region where pixels X5, X6, and X7 are located within the region included in the composite region X.

[0081] Here, by sharing the predetermined threshold described above 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 discontinuities in boundary regions caused by changing the method of generating predicted images for each region based on whether or not it is included in the composite region X, thereby improving encoding performance.

[0083] (Third embodiment) Hereinafter, 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 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 by a weighted average of a predicted image generated in the region included in the composite region X using a conventional HEVC prediction method (a predicted image generated based on undecoded reference pixels filled by copies) and a predicted image generated in the composite region X (a predicted image generated using the above-described predetermined prediction method).

[0085] In addition, in the encoding device 1 and 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 by a weighted average of a predicted image generated in the region included in the composite region X using a conventional HEVC prediction method (a predicted image generated based on undecoded reference pixels filled by copies) and a predicted image generated in the composite region X (a predicted image generated using the above-described predetermined prediction method), only when the above-described predetermined conditions are met.

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

[0087] The intra-prediction unit 13 and the intra-prediction unit 33 may be configured to use predetermined values ​​as weight coefficients, or they may be configured to calculate weight coefficients using the credibility of the decoded reference pixels when generating the predicted image.

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

[0089] Furthermore, 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 region between the region included in the composite region X and the region Y not included in the composite region X.

[0090] For example, the intra-prediction unit 13 and the intra-prediction unit 33 may calculate the weight coefficients so that near such boundary regions the weight coefficients of the predicted image generated using a conventional HEVC prediction method (a predicted image generated based on undecoded reference pixels filled by copies) are stronger, and in regions far from such boundary regions the weight coefficients of the predicted image generated in the composite region X (a predicted image generated using the above-described predetermined prediction method) are stronger.

[0091] (Other embodiments) As described above, the present invention has been explained by the embodiments described above, but the descriptions and drawings that constitute part of the disclosure in such embodiments should not be understood as limiting the present invention. Various alternative embodiments, examples, and operational techniques will become apparent to those skilled in the art from such disclosure.

[0092] Furthermore, although not specifically mentioned in the embodiments described above, a program may be provided that causes a computer to execute each of the processes performed by the encoding device 1 and decoding device 3 described above. Such a program may also be recorded on a computer-readable medium. Using a computer-readable medium, it is possible to install such a program on 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, but may be a recording medium such as a CD-ROM or DVD-ROM.

[0093] Alternatively, a chip may be provided comprising a memory for storing a program for implementing at least some of the functions in the encoding device 1 and decoding device 3 described above, and a processor for executing 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 / Quantization Section 16…Inverse quantization section / Inverse orthogonal transformation section 17…Local decoding image generation unit 18…Memory section 19... Entropy coding unit 3…Decoding device 31... Entropy Decoding Unit 32...Synthesis area determination section 33…Intra Prediction Unit 34…Inverse Quantization / Inverse Transformation Section 35...Local decoding image generation unit 36…Memory section

Claims

1. A decoding device configured to decode encoding target blocks obtained by dividing the original image into frame units that constitute a moving image, A first prediction unit generates a first predicted image by a first prediction process determined based on a prediction mode specified by flag information transmitted from the encoding side, A synthesis region determination unit configured to determine the synthesis region in the aforementioned block to be encoded, A second prediction unit generates a second predicted image by an intra-prediction process different from the first prediction process, which is determined without the transmission of any new flag information other than the flag information transmitted from the encoding side. The system comprises a prediction image synthesis unit that generates a prediction image included in the synthesis region by weighted averaging of the first prediction image and the second prediction image, The decoding device is characterized in that the predictive image synthesis unit determines the weights used for the weighted average for each pixel according to its position from the boundary region between the first predictive image and the second predictive image.

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

Images