Image synthesis apparatus, image synthesis method, and recording medium

1. An image synthesis apparatus for generating a composite image by synthesizing a second image with a part of a first image, the image synthesis apparatus comprising:

an image acquisition unit configured to acquire first group images including the first image and a plurality of different resolution images corresponding to the first image, and second group images including the second image and a plurality of different resolution images corresponding to the second image;

a frequency component calculation unit configured to calculate low-frequency components and high-frequency components from the first group images and the second group images; and

an image synthesis unit configured to generate the composite image on the basis of the low-frequency components of the first group images and the high-frequency components of the second group images.

2. The image synthesis apparatus according to claim 1 , wherein the image acquisition unit shrinks the low-frequency component of one of the first group images having a first resolution and the low-frequency component of one of the second group images having the first resolution, thereby generating one of the first group images having a second resolution less than the first resolution and one of the second group images having the second resolution.

3. The image synthesis apparatus according to claim 2 ,

wherein the image synthesis unit generates a temporary composite image for each resolution, and

wherein, after enlarging the generated temporary composite image having the second resolution and replacing a non-synthesis target region which is not a region of a synthesis target of the enlarged temporary composite image having the second resolution with a region corresponding to the non-synthesis target region in the first image having the first resolution, the image synthesis unit generates the temporary composite image having the first resolution by synthesizing a target high-frequency component in the synthesis target region so that a difference between a high-frequency component of the synthesis target region which is the region of the synthesis target of the enlarged temporary composite image having the second resolution and the target high-frequency component determined on the basis of a high-frequency component of the one of the second group images having the first resolution is minimized.

4. The image synthesis apparatus according to claim 3 , wherein the image synthesis unit sets one of the first group images having the lowest resolution among the first group images as the temporary composite image having the lowest resolution.

5. The image synthesis apparatus according to claim 4 , further comprising:

a mask image acquisition unit configured to acquire mask group images corresponding to the plurality of resolutions of the first group images, for defining the synthesis target region and the non-synthesis target region,

wherein the image synthesis unit uses each of the mask group images for each resolution to generate the temporary composite image for each resolution.

6. The image synthesis apparatus according to claim 5 , wherein the mask image acquisition unit divides one of the mask group images having the first resolution into blocks each having a predetermined number of pixels and generates one of the mask group images having the second resolution by replacing a block including the synthesis target region with a pixel of the synthesis target region and replacing a block not including the synthesis target region with a pixel of the non-synthesis target region.

7. The image synthesis apparatus according to claim 6 ,

wherein, for each resolution, the high-frequency component calculation unit calculates the high-frequency component of the first group images by subtracting the low-frequency component of the first group images from the first group images and calculates the high-frequency component of the second group images by subtracting the low-frequency component of the second group images from the second group images.

8. The image synthesis apparatus according to claim 4 ,

wherein, for each resolution, the high-frequency component calculation unit calculates the high-frequency component of the first group images by subtracting the low-frequency component of the first group images from the first group images and calculates the high-frequency component of the second group images by subtracting the low-frequency component of the second group images from the second group images.

9. The image synthesis apparatus according to claim 5 ,

wherein, for each resolution, the high-frequency component calculation unit calculates the high-frequency component of the first group images by subtracting the low-frequency component of the first group images from the first group images and calculates the high-frequency component of the second group images by subtracting the low-frequency component of the second group images from the second group images.

10. The image synthesis apparatus according to claim 3 , further comprising:

a mask image acquisition unit configured to acquire mask group images corresponding to the plurality of resolutions of the first group images, for defining the synthesis target region and the non-synthesis target region,

wherein the image synthesis unit uses each of the mask group images for each resolution to generate the temporary composite image for each resolution.

11. The image synthesis apparatus according to claim 10 , wherein the mask image acquisition unit divides one of the mask group images having the first resolution into blocks each having a predetermined number of pixels and generates one of the mask group images having the second resolution by replacing a block including the synthesis target region with a pixel of the synthesis target region and replacing a block not including the synthesis target region with a pixel of the non-synthesis target region.

12. The image synthesis apparatus according to claim 11 ,

wherein, for each resolution, the high-frequency component calculation unit calculates the high-frequency component of the first group images by subtracting the low-frequency component of the first group images from the first group images and calculates the high-frequency component of the second group images by subtracting the low-frequency component of the second group images from the second group images.

13. The image synthesis apparatus according to claim 10 ,

wherein, for each resolution, the high-frequency component calculation unit calculates the high-frequency component of the first group images by subtracting the low-frequency component of the first group images from the first group images and calculates the high-frequency component of the second group images by subtracting the low-frequency component of the second group images from the second group images.

14. The image synthesis apparatus according to claim 3 ,

wherein, for each resolution, the high-frequency component calculation unit calculates the high-frequency component of the first group images by subtracting the low-frequency component of the first group images from the first group images and calculates the high-frequency component of the second group images by subtracting the low-frequency component of the second group images from the second group images.

15. The image synthesis apparatus according to claim 2 ,

wherein, for each resolution, the high-frequency component calculation unit calculates the high-frequency component of the first group images by subtracting the low-frequency component of the first group images from the first group images and calculates the high-frequency component of the second group images by subtracting the low-frequency component of the second group images from the second group images.

16. The image synthesis apparatus according to claim 1 ,

wherein, for each resolution, the high-frequency component calculation unit calculates the high-frequency component of the first group images by subtracting the low-frequency component of the first group images from the first group images and calculates the high-frequency component of the second group images by subtracting the low-frequency component of the second group images from the second group images.

17. An image synthesis method to be performed by an image synthesis apparatus for generating a composite image by synthesizing a second image with a part of a first image, the image synthesis method comprising:

an image acquisition step of acquiring first group images including the first image and a plurality of different resolution images corresponding to the first image, and second group images including the second image and a plurality of different resolution images corresponding to the second image;

a frequency component calculation step of calculating low-frequency components and high-frequency components from the first group images and the second group images; and

an image synthesis step of generating the composite image on the basis of the low-frequency components of the first group images and the high-frequency components of the second group images.

18. A non-transitory recording medium recording an image synthesis program for operating a computer to generate a composite image by synthesizing a second image with a part of a first image, the image synthesis program for causing the computer to function as:

an image acquisition unit configured to acquire first group images including the first image and a plurality of different resolution images corresponding to the first image, and second group images including the second image and a plurality of different resolution images corresponding to the second image;

a frequency component calculation unit configured to calculate low-frequency components and high-frequency components from the first group images and the second group images; and

an image synthesis unit configured to generate the composite image on the basis of the low-frequency components of the first group images and the high-frequency components of the second group images.