Image processing apparatus for correcting distortion of image and image shooting apparatus for correcting distortion of shot image

• US 20050206753A1
• Filed: 03/17/2005
• Published: 09/22/2005
• Est. Priority Date: 03/19/2004
• Status: Active Grant

• Current Assignee: Casio Computer Company Limited
• Original Assignee: Casio Computer Company Limited
• Inventors: Sakurai, Keiichi, Makino, Tetsuji
• Granted Patent: US 7,619,663 B2
• Time in Patent Office: Days
• US Class Current: 348/241
• CPC Class Codes: G06T 3/00 Geometric image transformations in the plane of the image
• CPC Class Codes: G06T 3/403 Edge-driven scaling; Edge-based scaling
• CPC Class Codes: G06T 5/80 Geometric correction

Abstract

A digital camera acquires the image of an original including an original from a shot image acquired by shooting. The digital camera reduces the image of the original and corrects distortion of the reduced image which is originated from the characteristic of a lens. As the digital camera performs distortion correction on the reduced image, the number of arithmetic operations in distortion correction is reduced, making distortion correction simpler. The digital camera acquires a rectangle defined by the contour of the original, extracts the image of the original to acquire an original image before reduction, and acquires an associated projection-transformed image by affine transformation. The digital camera acquires pixel positions of the original image using an affine parameter, and acquires pixel positions of the image before distortion correction using a relational expression of distortion correction performed on the reduced image.

Claims

1. An image processing apparatus which corrects distortion of an image, and comprises:

a shot-image acquisition section which acquires a shot image of a subject to be shot, including a shooting target image which is an image portion corresponding to said subject to be shot;

a reduced-image acquisition section which acquires a reduced image that is said shot image with a reduced resolution;

a distortion information acquisition section which acquires distortion information indicative of distortion of said shooting target image based on said reduced image;

a projection parameter acquisition section which acquires a projection parameter for converting said shooting target image to an ideal distortion-free image based on said distortion information; and

a projection transformation section which produces a projection-transformed image by performing projection transformation on said shot image using said projection parameter.

2. The image processing apparatus according to claim 1, wherein distortion of said shooting target image includes linear distortion which occurs according to a shooting angle at a time of shooting said subject to be shot, and

said projection transformation is transformation for correcting said linear distortion.

3. The image processing apparatus according to claim 2, wherein distortion of said shooting target image includes distortion which occurs according to a characteristic of a lens used in shooting said subject to be shot, and

said distortion information acquisition section acquires a corrected reduced image by performing distortion correction on said reduced image according to said characteristic of said lens, and acquires distortion information indicative of linear distortion of said shooting target image based on said corrected reduced image.

4. The image processing apparatus according to claim 3, wherein said distortion information acquisition section acquires a shape of said projection-transformed image based on said corrected reduced image, and acquires distortion information indicative of linear distortion of said shooting target image based on said shape of said shooting target image and a real shape of said subject to be shot.

5. The image processing apparatus according to claim 3, wherein said distortion information acquisition section acquires a shape of said projection-transformed image based on said corrected reduced image, and acquires distortion information indicative of linear distortion of said shooting target image based on said shape of said shooting target image and a real shape of said subject to be shot.

6. The image processing apparatus according to claim 4, wherein said real shape of said subject to be shot is a rectangle, and

said distortion information acquisition section acquires a contour of said shooting target image based on said corrected reduced image, specifies four line portions of said contour, and acquires a shape of a trapezoid formed by said four line portions as said distortion information.

7. The image processing apparatus according to claim 6, wherein said real shape of said subject to be shot is a rectangle, and

said line portions are specified based on Hough transformation, and lines corresponding to a top side, a bottom side, a left side and a right side of said trapezoid are specified according to which directions to a center of said corrected reduced image angles of said line portions acquired by said Hough transformation correspond.

8. The image processing apparatus according to claim 1, wherein said projection transformation section performs said projection transformation at a same time as extracting said shooting target image from said shot image.

9. The image processing apparatus according to claim 1, wherein said projection transformation section performs said projection transformation in association with each pixel position constituting said projection-transformed image, specifies a position on said shot image which corresponds to said each pixel position on said projection-transformed image based on said projection parameter, and uses a pixel value on said shot image which corresponds to said specified position as a pixel value corresponding to said each pixel position on said projection-transformed image.

10. The image processing apparatus according to claim 9, wherein said projection transformation section computes said pixel value corresponding to each pixel position on said projection-transformed image by performing pixel interpolation based on a plurality of pixels near a position on said shot image specified based on said projection parameter.

11. The image processing apparatus according to claim 9, wherein a resolution of said projection-transformed image is lower than a resolution of said shot image.

12. The image processing apparatus according to claim 3, wherein said projection transformation section produces said projection-transformed image by performing distortion correction according to said characteristic of said lens at a same time as said projection transformation.

13. The image processing apparatus according to claim 1, wherein said subject to be shot is a sheet, and

said shooting target image is an image of an original on which what is written on said sheet is transferred.

14. The image processing apparatus according to claim 1, wherein said image processing apparatus is an image shooting apparatus (1) comprising a lens having a predetermined characteristic, an image pickup section which shoots a subject to be shot through said lens, thereby acquiring a shot image,

a shot image taken by said image pickup section is said shot image to be acquired by said shot-image acquisition section, and said projection-transformed image acquired by said projection transformation section is recorded.

15. An image shooting apparatus which corrects distortion of a shot image, comprising:

a lens having a predetermined characteristic;

an image pickup section which shoots a subject to be shot through said lens, thereby acquiring a shot image;

a corrected reduced-image acquisition section which acquires a corrected reduced image by reducing a resolution of said shot image and performing distortion correction according to said characteristic of said lens;

a distortion information acquisition section which acquires distortion information indicative of distortion at a time of shooting said subject to be shot based on said corrected reduced image; and

a projection transformation section which converts said shot image to an ideal distortion-free image based on said distortion information.

16. The image shooting apparatus according to claim 15, further comprising a display section (24) which displays said shot image, and

wherein said reduced-image acquisition section reduces said shot image in association with a display size of an image to be displayed by said display section.

17. The image shooting apparatus according to claim 15, further comprising a recording section which records a projection-transformed image produced by said projection transformation section.

18. An image processing method comprising:

a step of acquiring a shot image of a subject to be shot, including a shooting target image which is an image portion corresponding to said subject to be shot;

a step of acquiring a reduced image that is said shot image with a reduced resolution;

a step of acquiring distortion information indicative of distortion of said shooting target image based on said reduced image;

a step of acquiring a projection parameter for converting said shooting target image to an ideal distortion-free image based on said distortion information; and

a step of producing a projection-transformed image by performing projection transformation on said shot image using said projection parameter.

19. A program for allowing a computer to execute:

a procedure of acquiring a shot image of a subject to be shot, including a shooting target image which is an image portion corresponding to said subject to be shot;

a procedure of acquiring a reduced image that is said shot image with a reduced resolution;

a procedure of acquiring distortion information indicative of distortion of said shooting target image based on said reduced image;

a procedure of acquiring a projection parameter for converting said shooting target image to an ideal distortion-free image based on said distortion information; and

a procedure of producing a projection-transformed image by performing projection transformation on said shot image using said projection parameter.