Method for presenting fisheye-camera images

• US 7,042,508 B2
• Filed: 09/05/2002
• Issued: 05/09/2006
• Est. Priority Date: 07/26/2002
• Status: Expired due to Fees

• Current Assignee: Appro Technology, Inc.
• Original Assignee: Appro Technology, Inc.
• Inventors: Jan, Gwo-Jen, Chang, Chuang-Jan
• Primary Examiner(s): HO, TUAN V
• Application Number:
  US10/234,258
• Publication Number:
  US 20040046888A1
• Time in Patent Office: 1,342 Days
• Field of Search: 348/335, 348/36, 348/39, 348/143
• US Class Current: 348/335
• CPC Class Codes: G02B 13/06 Panoramic objectives; So-called "sky lenses" including panoramic objectives having reflecting surfaces
• CPC Class Codes: G06T 3/047 Fisheye or wide-angle transformations
• CPC Class Codes: H04N 17/002 for television cameras
• CPC Class Codes: H04N 23/698 for achieving an enlarged field of view, e.g. panoramic image capture
• CPC Class Codes: H04N 7/183 for receiving images from a single remote source

Abstract

The present invention is a method for presenting the fisheye-camera images. A calibration target with a concentric-and-symmetric pattern (PCT) is utilized to assist in parameterizing a fisheye camera (FIS) in order to ascertain the optical parameters comprising the principal point, the focal length constant and the projection function of the FIS. Hence, the position of an imaged point referring to the principal point on the image plane directly reflects its corresponding zenithal distance α and azimuthal distance β of the sight ray in space so as to normalize the imaged point onto a small sphere. Further according to the map projections in cartography capable of transforming the global geometry into flap maps, the interesting area in a field of view can be accordingly transformed by a proper projection method. The image transforming method disclosed in the invention is simple, low-cost, suitable to various FISs with different projection mechanisms and capable of transforming the fisheye-camera images for particular functions, such as the approach of normal human visual perception, video data encryption, and image compression/transformation with a high fidelity.

Claims

1. A method for presenting fisheye-camera images, which employs a plurality of known optical parameters comprising a principal point, a focal length constant and a projection function obtained from a parameterized fisheye camera in order to transform an original image shot by the parameterized fisheye camera into a transformed image, the method comprises:

calculating a principal distance ρ

between an imaged point and the principal point in the original image and defining an azimuthal distance β

of the imaged point;

deriving a zenithal distance α

of the imaged point according to the principal distance ρ

, the focal length constant and the projection function;

normalizing the imaged point onto a small sphere as a normalized imaged point according to the zenithal distance α and

the azimuthal distance β

; and

projecting the normalized imaged point onto a projection surface as a transformed imaged point by means of a map projection in cartography in order to form the transformed image.

2. The method according to claim 1, wherein the map projection is constructed by four elements comprising a light-source position, the projection surface, the orientation of the projection surface and the tangency of the projection surface.

3. The method according to claim 2, wherein the light-source position is selected from the group comprising a gnomonic projection, a stereographic projection and an orthographic projection.

4. The method according to claim 2, wherein the projection surface is selected from the group comprising a cylinder, a cone and a plane.

5. The method according to claim 2, wherein the orientation of the projection surface is selected from the group comprising a normal projection, a transverse projection and an oblique projection.

6. The method according to claim 2, wherein the tangency of the projection surface is selected from the group comprising a tangent projection and a secant projection.

7. The method according to claim 1, wherein the zenithal distance α

is the angle extending from an optical axis of the parameterized fisheye camera to an incident ray which images the imaged point.

8. The method according to claim 1, wherein the azimuthal distance β

is the angle of the imaged point surrounding an optical axis of the parameterized fisheye camera by referring to a prime meridian or a mapping domain of the prime meridian.

9. The method according to claim 1, wherein the center of the small sphere is located at a viewpoint of the parameterized fisheye camera.

10. The method according to claim 1, wherein the imaged point is located within a user-defined area in the original image.

11. A method for presenting fisheye-camera images, which employs a plurality of known optical parameters comprising a principal point, a focal length constant and a projection function obtained from a parameterized fisheye camera in order to transform an imaged point into a normalized imaged point, the method comprises:

calculating a principal distance ρ

which is the distance between the imaged point and the principal point in an original image shot by the parameterized fisheye camera and defining an azimuthal distance β

corresponding to the imaged point;

deriving a zenithal distance α

corresponding to the imaged point according to the principal distance ρ

, the focal length constant and the projection function; and

normalizing the imaged point onto a small sphere as the normalized imaged point according to the zenithal distance α and

the azimuthal distance β

.

12. The method according to claim 11, wherein the zenithal distance α

is the angle extending from an optical axis of the parameterized fisheye camera to an incident ray which images the imaged point.

13. The method according to claim 11, wherein the azimuthal distance β

is the angle of the imaged point surrounding an optical axis of the parameterized fisheye camera by referring to a prime meridian or a mapping domain of the prime meridian.

14. The method according to claim 11, wherein the center of the small sphere is located at a viewpoint of the parameterized fisheye camera.

15. A method for presenting fisheye-camera images, which employs a plurality of known optical parameters comprising a principal point, a focal length constant and a projection function obtained from a parameterized fisheye camera in order to transform an original image shot by the parameterized fisheye camera into a panorama, the method comprises:

calculating a principal distance ρ

between an imaged point and the principal point in the original image and defining an azimuthal distance β

of the imaged point;

deriving a zenithal distance α

of the imaged point according to the principal distance ρ

, the focal length constant and the projection function;

normalizing the imaged point onto a small sphere as a normalized imaged point according to the zenithal distance α and

the azimuthal distance β

; and

projecting the normalized imaged point onto a cylindrical surface as a transformed imaged point by means of a gnomonic projection in cartography in order to form the panorama.

16. The method according to claim 15, wherein an orientation of the projection surface is selected from the group comprising a normal projection, a transverse projection and an oblique projection.

17. The method according to claim 15, wherein a tangency of the projection surface is selected from the group comprising a tangent projection and a secant projection.

18. The method according to claim 15, wherein the zenithal distance α

is the angle extending from an optical axis of the parameterized fisheye camera to an incident ray which images the imaged point.

19. The method according to claim 15, wherein the azimuthal distance β

is the angle of the imaged point surrounding an optical axis of the parameterized fisheye camera by referring to a prime meridian or a mapping domain of the prime meridian.

20. The method according to claim 15, wherein the center of the small sphere is located at a viewpoint of the parameterized fisheye camera.

21. The method according to claim 15, wherein the imaged point is located within a user-defined area in the original image.

22. A method for presenting fisheye-camera images, which employs a plurality of known optical parameters comprising a principal point, a focal length constant and a projection function obtained from a parameterized fisheye camera in order to transform an original image shot by the parameterized fisheye camera into a perspective-corrected image, the method comprises:

calculating a principal distance ρ

between an imaged point and the principal point in the original image and defining an azimuthal distance β

of the imaged point;

deriving a zenithal distance α

of the imaged point according to the principal distance ρ

, the focal length constant and the projection function;

normalizing the imaged point onto a small sphere as a normalized imaged point according to the zenithal distance α and

the azimuthal distance β

; and

projecting the normalized imaged point onto a plane as a transformed imaged point by means of a gnomonic projection in cartography in order to form the perspective-corrected image.

23. The method according to claim 22, wherein an orientation of the projection surface is selected from the group comprising a normal projection, a transverse projection and an oblique projection.

24. The method according to claim 22, wherein a tangency of the projection surface is selected from the group comprising a tangent projection and a secant projection.

25. The method according to claim 22, wherein the zenithal distance α

is the angle extending from an optical axis of the parameterized fisheye camera to an incident ray which images the imaged point.

26. The method according to claim 22, wherein the azimuthal distance β

is the angle of the imaged point surrounding an optical axis of the parameterized fisheye camera by referring to a prime meridian or a mapping domain of the prime meridian.

27. The method according to claim 22, wherein the center of the small sphere is located at a viewpoint of the parameterized fisheye camera.

28. The method according to claim 22, wherein the imaged point is located within a user-defined area in the original image.