Warping of focal images to correct correspondence error

• US 6,148,120 A
• Filed: 10/30/1997
• Issued: 11/14/2000
• Est. Priority Date: 10/30/1997
• Status: Expired due to Term

• Current Assignee: Cognex Corporation
• Original Assignee: Cognex Corporation
• Inventors: Sussman, Michael
• Primary Examiner(s): Boudreau, Leo H.
• Assistant Examiner(s): SHERALI, ISHRAT I
• Application Number:
  US08/961,404
• Time in Patent Office: 1,111 Days
• Field of Search: 382/284, 382/255, 382/154, 382/153, 382/294, 382/293, 382/106, 382/263, 382/289-299, 356/376, 356/375, 356/394, 356/400-401, 356/2-3, 356/3.01, 359/368, 359/629, 348/135, 250/559.22, 250/201.4-201.6, 250/201.7, 250/559.31, 250/559.23, 250/559.38, 250/227.2, 250/307, 378/98
• US Class Current: 382/293
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 7/571 from focus
• CPC Class Codes: G06V 20/64 Three-dimensional objects

Abstract

The invention corrects correspondence error among multiple images taken at different focal distances with non-telecentric optical systems, and is particularly useful in focal gradient analysis range imaging systems.

Claims

1. A method for obtaining a range image using depth from focal gradient analysis, the method including:

acquiring a near reflectance image;

using a focus operator to obtain a near focal image;

acquiring a farther reflectance image;

using a focus operator to obtain a farther focal image;

warping the farther focal image so as to decrease correspondence error of the farther focal image with respect to the near focal image, thereby providing a warped farther focal image; and

range normalizing the near focal image and the warped farther focal image so as to provide a range image.

2. The method of claim 1, wherein warping includes scaling the farther focal image and translating the farther focal image.

3. The method of claim 1, wherein warping includes scaling the farther focal image.

4. The method of claim 1, wherein warping includes mapping and resampling.

5. The method of claim 4, wherein mapping includes locating a point in an input image which corresponds to a particular point to be generated for inclusion in an output image.

6. The method of claim 5, wherein the point in the input image is at an off-pixel-grid location.

7. The method of claim 5, wherein the point in the input image is at a pixel-grid location.

8. The method of claim 4, wherein resampling includes interpolation.

9. The method of claim 5, wherein resampling includes reading four pixels from an input image.

10. The method of claim 8, wherein interpolation is bi-linear interpolation.