JP7104101B2 - Encoding device, decoding device and program - Google Patents

Description

The present invention relates to a coding device, a decoding device and a program.

H. In the moving image coding method represented by 265 / HEVC (High Efficiency Video Coding), two types of predictions are performed: inter-prediction using temporal correlation between frames and intra-prediction using spatial correlation within frames. It is configured to output a stream obtained by performing orthogonal conversion processing, loop filtering processing, and entropy coding processing after performing prediction while switching to generate a residual signal.

In intra prediction in HEVC, a total of 35 types of modes such as Planar prediction, DC prediction, and direction prediction are prepared, and it is configured to perform intra prediction using adjacent decoded reference pixels according to the mode determined by the encoder. Has been done.

Here, in the intra prediction, in the CU in which there is no adjacent decoded reference pixel such as the CU (Coding Unit) located at the upper left in the frame, the specified value (“512” for a 10-bit moving image). It is configured to create a reference pixel to be used when generating a predicted image by the process of filling in.

Further, in the conventional HEVC, since the encoding process is performed in the raster scan order from the upper left, the reference pixel may not be decoded. In such a case, the predicted image is generated by using the value obtained by extrapolating the nearest decoded reference pixel to the 0th order.

The CU is divided into a plurality of blocks (TU: Transfer Unit) and subjected to orthogonal transformation processing. In HEVC, the intra-prediction mode indicating the type of intra-prediction to be applied is common within the CU, and the prediction is performed using the intra-prediction mode common to a plurality of TUs.

In the intra prediction, as shown in FIG. 7, the reference pixel N located at the lower left or upper right of CU # X is often not decoded due to the encoding process in the raster scan order. In such a case, the reference pixel N is not decoded. When the direction is predicted from the direction in which the reference pixel exists, there is a problem that the prediction accuracy is lowered and the coding efficiency is lowered.

Hereinafter, such a problem will be specifically described with reference to FIGS. 8 (a) to 8 (d). FIG. 8 shows an example of intra-prediction in conventional HEVC.

In such an example, as shown in FIG. 8A, as in the case of the example of FIG. 7, all the reference pixels of CU # A1 (the upper left CU in the frame) have been decoded. Similarly, as shown in FIG. 8C, all the reference pixels of CU # A3 (CU at the lower left in the frame) have been decoded.

On the other hand, as shown in FIG. 8B, the reference pixels W1 to W3 located in CU # A1 have been decoded, but the reference pixels B1 to B4 located in CU # A3 have been decoded. Therefore, it cannot be used as a reference pixel when generating a predicted image of CU # A2 (CU in the upper right of the frame) as it is.

Therefore, in the conventional HEVC, as shown in FIG. 8B, the value of the reference pixel W1 located at the bottom of the decoded reference pixels W1 to W3 located in the CU # A1 is set in the CU # A3. It is specified to copy to undecoded reference pixels B1 to B4 located in the same column of.

Similarly, in the conventional HEVC, as shown in FIG. 8D, the value of the reference pixel B1 located at the bottom of the decoded reference pixels B1 to B3 located in the CU # A3 is set to the value of the CU # A3. It is specified to copy to the undecrypted reference pixel P3 located in the same row in the lower CU.

Therefore, when the direction prediction is performed from the lower left to the upper right as in the example of FIG. 8, most of the generated predicted images are composed of undecoded reference pixels filled with copies, so that the prediction accuracy is high. There is a problem that it is lowered and the coding efficiency is lowered.

In order to solve such a problem, in the intra-prediction in which the TU division is performed, the coding processing order for a plurality of TUs existing in the CU is the raster scan order (for example, Z type), as well as the U type and the X type. There is known a technique for improving the prediction accuracy by giving a degree of freedom in the coding order such as (see Non-Patent Document 1).

Mochizuki et al., "Applied intra-prediction method based on average value coordinates", IPSJ Research Report, vol, 2012-AVM-77, No. 12

However, in the technique specified in Non-Patent Document 1 described above, it is necessary to transmit a flag as to what kind of coding processing order is used for each CU, so that the amount of information to be transmitted increases. , In order to select which coding processing order is better from all coding processing orders, it is necessary to try all combinations on the coding device side, which increases the calculation time on the coding device side. There was a problem.

Therefore, the present invention has been made to solve the above-mentioned problems, and predicts without increasing the amount of information transmitted by the encoding device and without increasing the calculation time on the encoding device side. An object of the present invention is to provide a coding device, a decoding device, and a program capable of improving accuracy and coding efficiency.

The first feature of the present invention is a coding device configured to divide the original image of each frame constituting the moving image into coding target blocks and encode the original image, based on the intra prediction mode. Based on a composite area determination unit configured to determine a composite region in which a predicted image is generated from adjacent pixels that have not been decoded in the coded block, and whether or not the predicted image is included in the composite region. The gist is to include an intra-prediction unit configured to change the method of generating a prediction image of each region.

A second feature of the present invention is a decoding device configured to divide an original image in frame units constituting a moving image into blocks to be encoded and decode it, and based on the intra prediction mode, the above-mentioned Each region is based on a composite region determination unit configured to determine a composite region in which a predicted image is generated from adjacent pixels that have not been decoded in the coded block, and whether or not the predicted image is included in the composite region. The gist is to include an intra-prediction unit configured to change the method of generating the prediction image of the above.

A third feature of the present invention is a program for making a computer function as a coding device according to the first or second feature described above.

A fourth feature of the present invention is a program for making a computer function as a decoding device according to the first or second feature described above.

According to the present invention, a coding device capable of improving prediction accuracy and coding efficiency without increasing the amount of information transmitted by the coding device and without increasing the calculation time on the coding device side. , Decoding devices and programs can be provided.

FIG. 1 is a functional block diagram of the coding apparatus 1 according to the first embodiment. FIG. 2 is a diagram showing an example of how a predicted image is generated in the first embodiment. FIG. 3 is a diagram showing an example of how a predicted image is generated in the first embodiment. FIG. 4 is a functional block diagram of the decoding device 3 according to the first embodiment. FIG. 5 is a flowchart showing the operation of the coding device 1 and the decoding device 3 according to the first embodiment. FIG. 6 is a diagram showing an example of how a predicted image is generated in the second embodiment. FIG. 7 is a diagram showing an example of how a predicted image is generated in conventional HEVC. FIG. 8 is a diagram showing an example of how a predicted image is generated in conventional HEVC.

(First Embodiment)
Hereinafter, the coding device 1 and the decoding device 3 according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 5. Here, the coding device 1 and the decoding device 3 according to the present embodiment are configured to correspond to the intra prediction in HEVC.

The coding device 1 according to the present embodiment is configured to divide the original image of each frame constituting the moving image into coding target blocks and encode the original image. In the present embodiment, it is assumed that all the pixels adjacent to the left side and the upper side of the CU to be encoded have been decoded.

Further, the coding device 1 according to the present embodiment may be configured so that the CU can be divided into a plurality of TUs. Therefore, in the present embodiment, the coded block may be a CU or a TU. Hereinafter, in the present embodiment, a case where CU is used as the coded block will be described as an example.

Further, in the present embodiment, as an example, a case where the raster scan order (Z type as shown in FIGS. 7 and 8) used in the conventional HEVC is used as the coding order and the decoding order of the CU is taken as an example. As the coding order and decoding order, other coding order and decoding order such as U type and X type may be used.

As shown in FIG. 1, the coding apparatus 1 according to the present 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, and orthogonal transformation. It includes a quantization unit 15, an inverse orthogonal transformation / inverse quantization unit 16, a locally decoded image generation unit 17, a memory unit 18, and an entropy coding unit 19.

The intra prediction mode determination unit 11 is configured to determine the optimum intra prediction mode to be applied to the CU.

The composite region determination unit 12 is configured to determine the composite region X in which the predicted image is generated from the adjacent pixels that have not been decoded in the CU, based on the intra prediction mode determined by the intra prediction mode determination unit 11. There is.

Specifically, as shown in FIG. 2, the composite region determination unit 12 is in 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 (that is, from the lower left to the upper right). In CU # A2), the composite region X in which the predicted image is generated from the adjacent pixels B1 to B4 that have not been decoded may be determined.

The present invention is also applied to the case where the direction of the intra prediction mode determined by the intra prediction mode determination unit 11 is the direction from the upper right to the lower left (that is, the direction prediction is performed from the upper right to the lower left). Although it is possible, the following is an example of 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 (that is, the direction is predicted from the lower left to the upper right). It will be explained by listing in.

In addition, in the figure of this specification, the arrow indicating the direction (prediction direction) of the intra prediction mode is assumed to go from the pixel to be the target of the intra prediction to the reference pixel as described in the HEVC standard (the same applies hereinafter). ..

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

Specifically, as shown in FIG. 3A, the intra prediction unit 13 includes a region not included in the composite region X in CU # A2 (that is, a region in which reference pixels W1 to W3 have been decoded). In Y, the predicted image is generated based on the decoded reference pixels W1 to W3 by using the intra prediction mode determined by the intra prediction mode determining unit 11.

On the other hand, as shown in FIG. 3B, the intra prediction unit 13 defines in advance in the region included in the composite region X (that is, the region in which the reference pixels B2 to B4 have not been decoded) in the CU # A2. It is configured to generate a predicted image using the predicted prediction method.

Here, examples of the predetermined prediction method include an intra prediction such as DC prediction and Planar prediction, and a prediction method for generating a prediction image by averaging the values of adjacent decoded reference pixels.

If the coding device 1 and the decoding device 3 determine the prediction method in advance, the coding device 1 can use the prediction method for the decoding device 3 regardless of which prediction method is used. There is no need to transmit the new flag to indicate.

Further, since the composite region determined by the composite region determination unit 12 can be uniquely determined depending on the direction of the intra prediction mode and whether or not the adjacent pixel has been decoded, the encoding device 1 to the decoding device 3 However, it is not necessary to newly transmit a flag indicating which region the composite region is.

For example, as shown in FIG. 3B, the intra prediction unit 13 uses the Planar prediction at the position of the pixel X1 in the region included in the composite region X in the CU # A2 to use the Planar prediction to make the pixel W3 and the pixel D1. , Pixels D2 and pixels D4 may be combined to generate a predicted image. Here, the value of the pixel B4 is copied to the pixel D4, and the value of the pixel W1 is copied to the pixel B4.

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.

The orthogonal transformation / quantization unit 15 is configured to perform orthogonal transformation processing and quantization processing on the residual signal generated by the residual signal generation unit 14 to generate a quantized conversion coefficient. ..

The inverse orthogonal transformation / inverse quantization unit 16 performs the inverse quantization processing and the inverse orthogonal transformation processing again on the quantized conversion coefficient generated by the orthogonal transformation / quantization unit 15, and the quantized residue. It is configured to generate a difference signal.

The locally decoded image generation unit 17 generates a locally decoded image by adding the predicted image generated by the intra prediction unit 13 to the quantized residual signal generated by the inverse orthogonal transformation / inverse quantization unit 16. It is configured to do.

The memory unit 18 is configured to hold the locally decoded image generated by the locally decoded image generation unit 17 so as to be available as a reference image.

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 the quantized conversion coefficient and output the stream. There is.

Further, the decoding device 3 according to the present embodiment is configured to divide the original image of each frame constituting the moving image into CUs and decode it. Further, the decoding device 3 according to the present embodiment is configured so that the CU can be divided into a plurality of TUs, similarly to the coding device 1 according to the present embodiment.

As shown in FIG. 4, the decoding device 3 according to the present embodiment includes an entropy decoding unit 31, a synthesis region determination unit 32, an intra prediction unit 33, an inverse quantization / inverse conversion unit 34, and a locally decoded image generation. A unit 35 and a memory unit 36 are provided.

The entropy decoding unit 31 is configured to decode conversion coefficients, flag information, and the like from the stream output from the encoding device 1. Here, the conversion coefficient is a quantized conversion coefficient obtained as a signal encoded by dividing the original image in frame units into CUs by the coding device 1. In addition, the flag information includes accompanying information such as a prediction mode.

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

Specifically, as shown in FIG. 2, the synthesis region determination unit 32 is in the case where the direction of the intra prediction mode output by the entropy decoding unit 31 is from the lower left to the upper right (that is, from the lower left to the upper right). When direction prediction is performed), the composite region X in which the predicted image is generated from the adjacent pixels B1 to B4 that have not been decoded may be determined in CU # A2.

The intra prediction unit 33 may be configured to generate a prediction image by 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.

Specifically, the intra prediction unit 33, like the intra prediction unit 13, determines a method of generating a predicted image of each region based on whether or not it is included in the composite region X determined by the composite region determination unit 12. It is configured to change.

For example, as shown in FIG. 3A, the intra prediction unit 33 sets the region Y not included in the composite region X (that is, the region in which the reference pixels W1 to W3 have been decoded) Y in the CU # A2. The intra prediction mode output by the entropy decoding unit 31 is used to generate a predicted image based on the decoded reference pixels W1 to W3.

On the other hand, as shown in FIG. 3B, the intra prediction unit 33 described above in the region included in the composite region X (that is, the region in which the reference pixels B2 to B4 have not been decoded) in the CU # A2. It is configured to generate a prediction image using a predetermined prediction method.

The inverse quantization / inverse transformation unit 34 performs the inverse quantization processing and the inverse transformation processing (for example, the inverse orthogonal transformation processing) on the quantized conversion coefficient output by the entropy decoding unit 31, and the residual. It is configured to generate a signal.

The locally decoded image generation unit 35 is configured to generate a locally decoded image by adding the predicted image generated by the intra prediction unit 33 and the residual signal generated by the inverse quantization / inverse conversion unit 34. There is.

The memory unit 36 is configured to hold the locally decoded image generated by the locally decoded image generation unit 35 so as to be available as a reference image for intra-prediction and inter-prediction.

FIG. 5 shows a flowchart for explaining an example of an operation of generating a predicted image by the coding device 1 and the decoding device 3 according to the present embodiment.

First, with reference to FIG. 5, an example of an operation of generating a predicted image by the coding apparatus 1 according to the present embodiment will be described.

As shown in FIG. 5, in step S101, the coding apparatus 1 determines the optimum intra prediction mode to be applied to the CU.

In step S102, the coding apparatus 1 determines the composite region X in which the predicted image is generated from the adjacent pixels that have not been decoded in the CU, based on the intra prediction mode determined in step S101.

In step S103, the coding apparatus 1 determines whether or not the region for generating the predicted image is included in the composite region in the CU. If "No", this operation proceeds to step S104, and if "Yes", this operation proceeds to step S105.

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.

In step S105, the coding apparatus 1 generates a prediction image using the above-mentioned predetermined prediction method.

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.

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

In step S102, the decoding device 3 determines the composite region X in which the predicted image is generated from the adjacent pixels that have not been decoded in the CU, based on the intra prediction mode determined in step S101.

In step S103, the decoding device 3 determines whether or not the region for generating the predicted image is included in the composite region in the CU. If "No", this operation proceeds to step S104, and if "Yes", this operation proceeds to step S105.

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.

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

According to the encoding device 1 and the decoding device 3 according to the present embodiment, when an undecoded pixel is included in the reference destination in the direction (prediction direction) of the intra prediction mode, the adjacent decoded reference pixel is copied. By synthesizing the predicted image generated using the reference pixels interpolated in step 1 and the predicted image generated using the predetermined prediction method, a new predicted image can be generated, thereby suppressing a decrease in prediction accuracy. ..

(Second Embodiment)
Hereinafter, with reference to FIG. 6, the coding device 1 and the decoding device 3 according to the second embodiment of the present invention are different from the coding device 1 and the decoding device 3 according to the first embodiment described above. This will be explained with a focus on.

In the coding apparatus 1 according to the present embodiment, the intra prediction unit 13 determines that a predetermined condition is satisfied in the boundary region between the region included in the composite region X and the region Y not included in the composite region X. It is configured to apply a smoothing filter to the predicted image of such a boundary region.

Similarly, in the decoding device 3 according to the present embodiment, the intra prediction unit 33 satisfies a predetermined condition in the boundary region between the region included in the composite region X and the region Y not included in the composite region X. It is configured to apply a smoothing filter to the predicted image of such a boundary region.

For example, in the example of FIG. 6, the boundary region includes pixels X1, X2, X3, X4 in the region included in the composite region X and pixels Y1, Y2, Y3 in the region Y not included in the composite region X. The area where it is located is applicable.

Further, as a predetermined condition, the discontinuity in the boundary region is higher than the predetermined threshold value. Here, as an evaluation of the discontinuity, for example, a method of expressing by a linear combination such as a difference in the horizontal direction, a difference in the vertical direction, and a difference in the diagonal direction can be mentioned.

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

For example, in the example of FIG. 6, when the value of the evaluation of discontinuity in the boundary region is higher than the predetermined threshold value, the intra prediction unit 13 and the intra prediction unit 33 have pixels in the region included in the composite region X. The smoothing filter is applied to the predicted image of the region where the pixels Y1, Y2, and Y3 in the region Y not included in the X1, X2, X3, X4 and the composite region X are located.

In the example of FIG. 6, the intra prediction unit 13 and the intra prediction unit 33 also apply the smoothing filter to the prediction image of the region where the pixels X5, X6, and X7 are located in the region included in the composite region X. It is configured as follows.

Here, by sharing the above-mentioned predetermined threshold value between the coding device 1 and the decoding device 3, it is not necessary to transmit a new flag from the coding device 1 to the decoding device 3.

According to the coding device 1 and the decoding device 3 according to the present embodiment, the discontinuity of the boundary region caused by changing the method of generating the predicted image of each region based on whether or not it is included in the composite region X. Can be reduced and the coding performance can be improved.

(Third Embodiment)
Hereinafter, with reference to FIG. 6, the coding device 1 and the decoding device 3 according to the third embodiment of the present invention will be referred to as the coding device 1 and the decoding device 3 according to the first and second embodiments described above. The difference will be explained by paying attention to the difference.

In the coding device 1 and the decoding device 3 according to the present embodiment, the intra prediction unit 13 and the intra prediction unit 33 are predicted images generated by using the prediction method in the conventional HEVC in the region included in the synthesis region X (the prediction image (). Predicted by weighted average of predicted image (predicted image generated based on undecoded reference pixels filled by copy) and predicted image generated in synthetic region X (predicted image generated using the predetermined prediction method described above). It is configured to generate an image.

In the coding device 1 and the decoding device 3 according to the present embodiment, the intra prediction unit 13 and the intra prediction unit 33 are conventional in the region included in the synthesis region X only when the above-mentioned predetermined conditions are satisfied. A prediction image generated using the prediction method in HEVC (a prediction image generated based on undecoded reference pixels filled by copying) and a prediction image generated in the composite region X (predetermined prediction method described above). It may be configured to generate a predicted image by a weighted average of the predicted image) generated using it.

In the coding device 1 and the decoding device 3 according to the present embodiment, the intra prediction unit 13 and the intra prediction unit 33 may be configured to calculate the weighting coefficient used when calculating the weighted average.

The intra prediction unit 13 and the intra prediction unit 33 may be configured to use a predetermined value as the weighting coefficient, or the weighting coefficient may be used by using the credit rating of the decoded reference pixel when generating the predicted image. May be configured to calculate.

In the example of FIG. 3B, the decoded reference pixels W1 to W4 have a high credit rating, and the reference pixels B1 to B4 generated by copying have a low credit rating. Further, when the credit rating of the reference pixel B1 and the credit rating of the reference pixel B4 are compared, the credit rating of the reference pixel B4, which is closer to the copy source, is higher.

Further, the intra prediction unit 13 and the intra prediction unit 33 calculate such a weighting coefficient 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. It may be configured in.

For example, the intra prediction unit 13 and the intra prediction unit 33 may generate a prediction image (prediction generated based on undecoded reference pixels filled by copying) in the vicinity of the boundary region using a prediction method in conventional HEVC. The weight coefficient of the image) is calculated to be strong, and in the region away from the boundary region, the weight of the predicted image (predicted image generated by using the predetermined prediction method described above) generated in the composite region X is performed. It may be calculated so that the coefficient becomes stronger.

(Other embodiments)
As mentioned above, the invention has been described by the embodiments described above, but the discourses and drawings that form part of the disclosure in such embodiments should not be understood as limiting the invention. Such disclosure will reveal to those skilled in the art various alternative embodiments, examples and operational techniques.

Further, although not particularly mentioned in the above-described embodiment, a program for causing a computer to execute each process performed by the above-mentioned encoding device 1 and decoding device 3 may be provided. The program may also be recorded on a computer-readable medium. Computer-readable media can be used to install such programs on computers. 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, for example, a recording medium such as a CD-ROM or a DVD-ROM.

Alternatively, even if a chip composed of a memory for storing a program for realizing at least a part of the functions in the encoding device 1 and the decoding device 3 described above and a processor for executing the program stored in the memory is provided. good.

1 ... Encoding device 11 ... Intra prediction mode determination unit 12 ... Synthesis region determination unit 13 ... Intra prediction unit 14 ... Residual signal generation unit 15 ... Orthogonal transformation / quantization unit 16 ... Inverse quantization unit / inverse orthogonal transformation unit 17 ... Locally decoded image generation unit 18 ... Memory unit 19 ... Entropy coding unit 3 ... Decoding device 31 ... Entropy decoding unit 32 ... Synthesis area determination unit 33 ... Intra prediction unit 34 ... Inverse quantization / inverse transformation unit 35 ... Locally decoded image Generation unit 36 ... Memory unit

Claims (2)

A decoding device configured to decode a coded block obtained by dividing an original image in frame units constituting a moving image.
A first prediction unit that generates a first prediction image by a first prediction process that is determined based on an intra prediction mode specified by flag information transmitted from the coding side .
A composite area determination unit configured to determine a composite region in the coded block, and a composite region determination unit.
The second prediction process , which is different from the first prediction process and is determined without transmitting new flag information in addition to the flag information transmitted from the coding side, produces a second prediction image. The second predictor to be generated and
It includes a predictive image compositing unit that generates a predictive image included in the composite region by a weighted average of the first predictive image and the second predictive image.
The predictive image synthesizing unit is a decoding device, characterized in that the weight used for the weighted average is determined for each pixel according to the position of the pixels included in the synthesizing region. A program for operating a computer as the decoding device according to claim 1.

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