Correcting lens distortion

• US 6,002,525 A
• Filed: 07/06/1998
• Issued: 12/14/1999
• Est. Priority Date: 07/06/1998
• Status: Expired due to Term

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Intel Corporation
• Inventors: Poulo, Richard J., Gorman, Walter L.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): THOMPSON, TIMOTHY J
• Application Number:
  US09/110,805
• Time in Patent Office: 526 Days
• Field of Search: 359/642, 382/292, 382/254, 382/255, 382/275, 345/427, 345/425, 345/436
• US Class Current: 359/642
• CPC Class Codes: G01M 11/0221 by determining the optical axis or position of lenses
• CPC Class Codes: G01M 11/0264 by using targets or reference patterns
• CPC Class Codes: G02B 27/0025 for optical correction, e.g. distorsion, aberration

Abstract

Lens distortion may be corrected using a least squares curve fitting method to determine a straight line approximation for the curvature caused by lens distortion. An image made of a rectangular shape formed from a series of circles may be utilized as the target for a picture which may be taken to calibrate for lens distortion. The deviation of each of the straight lines caused by the lens distortion can be calculated assuming that the optical axis is centered on the image. The presumed optical axis can be adjusted towards the sides of the rectangle with the lower values of distortion coefficient. When the lines agree the optical axis has been located. The deviation is measured perpendicularly from a best fit straight line approximation.

Claims

1. A method of evaluating lens distortion comprising:

taking a picture of a rectangular pattern of closed geometric shapes;

using an equation to curve fit a line to the curvature caused by the lens distortion; and

solving the equation for the minimum deviation of the best fit line from that curvature, the deviation being measured in a direction perpendicular to the best fit line.

2. The method of claim 1 including talking a picture of a rectangular pattern of circles and using a least squares equation to curve fit a line to the curvature caused by lens distortion.

3. The method of claim 1 including using a plurality of serially arranged circles to create the rectangular pattern.

4. The method of claim 3 including calculating the centroid of each circle.

5. The method of claim 4 including calculating the deviation of each line of the rectangle.

6. The method of claim 5 including assuming the optical axis is centered on the image.

7. The method of claim 5 including applying a lens distortion correction until the minimum deviation is achieved for each line of the rectangle.

8. The method of claim 7 including adjusting the presumed optical axis to make the deviations substantially equal.

9. The method of claim 8 including repeating the process for additional images.

10. A method for determining the location of the optical axis of a lens comprising:

determining the lens distortion coefficients for each side of a closed geometrical shape having sides;

applying the lens distortion coefficient until a minimum deviation is achieved for each side; and

determining whether the lens distortion coefficients for the sides are substantially equal.

11. The method of claim 10 including assuming the optical axis is centered on the image.

12. The method of claim 11 including correcting for the true position of the optical axis by picking a new presumed optical axis displaced towards a side with a lower value of the lens distortion coefficient than another side.

13. An element comprising a machine readable storage medium storing instructions that cause a computer to:

calculate the centroid of a circle,

use a least squares equation to determine a best fit line approximation for the curvature caused by lens distortion; and

solve the least squares equation for the minimum deviation of the best fit line from that curvature, the deviation being measured in a direction perpendicular to the best fit line.

14. An element comprising a machine readable storage medium storing instructions that cause a computer to:

calculate the lens distortion coefficients for each side of a closed geometrical shape;

apply the lens distortion coefficients until a minimum deviation is achieved for each side; and

determine whether the lens distortion coefficients for the sides are substantially equal.

15. A method of evaluating lens distortion comprising:

determining a best fit line approximation for the curvature caused by lens distortion;

solving the equation for the minimum deviation of the best fit line from that curvature, the deviation being measured in a direction perpendicular to best fit line;

applying a lens distortion correction until the minimum deviation is achieved for each line; and

adjusting the presumed optical axis to make the deviation substantially equal.

16. The method of claim 15 including taking a picture of a rectangular pattern of circles and using a least squares equation to curve fit a line to the curvature caused by lens distortion.

17. The method of claim 16 including using a plurality of serially arranged circles to create the rectangular pattern.

18. The method of claim 17 including calculating the centroid of each circle.

19. The method of claim 18 including calculating the deviation of each line of the rectangle.

20. The method of claim 15 including repeating the process for additional images.