Calibration methods for thick lens model

• US 9,781,412 B2
• Filed: 02/04/2015
• Issued: 10/03/2017
• Est. Priority Date: 02/04/2015
• Status: Active Grant

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Tu, Xue, Li, Pingshan, Berestov, Alexander
• Primary Examiner(s): Wang, Xi
• Application Number:
  US14/614,268
• Publication Number:
  US 20160227206A1
• Time in Patent Office: 972 Days
• Field of Search: 348187, 3482403, 356124, 3562392, 356676, 3187, 32403, 359676
• CPC Class Codes: G06T 7/80 Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration
• CPC Class Codes: H04N 17/002 for television cameras

Abstract

The thick lens calibration method enables better calibration of complex camera devices such as devices with thick lens systems. The thick lens calibration method includes a two step process of calibrating using the distance between a second nodal point and an image sensor, and calibrating using the distance between the first and second nodal point.

Claims

1. A method programmed in a non-transitory memory of a device comprising:

a. calibrating the device using a first distance between a second nodal point and an image sensor; and

b. calibrating the device using a second distance between a first nodal point and the second nodal point, wherein calibrating the device includes moving one or more lenses based on the second nodal point and the image sensor, wherein calibrating further comprises utilizing a distance relationship, where there is a same object position but different lens settings, wherein calibrating further comprises utilizing a magnification factor, a distance to an object, and calibration information, wherein the magnification factor is calculated using a checkerboard object at a certain distance and taking pictures with the different lens settings, and the magnification factor is calculated by measuring distances between circle centers in the checkerboard object, wherein measuring the distances between the circle centers includes cropping out a patch that contains a circle, the patch is convolved with itself, a position of the maximal convolution result is determined, and a distance between the circle centers is measured.

2. The method of claim 1 wherein the calibrating further comprises taking a picture of a checkerboard pattern.

3. The method of claim 1 wherein the calibrating further comprises calculating a magnification factor by measuring a first distance of two corner points on a real checkerboard and a second distance of two corner points on an image of the checkerboard.

4. The method of claim 3 wherein corner detection is used to locate rough position of the corner points.

5. The method of claim 3 wherein calibrating further comprises calculating the first distance between the second nodal point and the image sensor using the magnification factor.

6. The method of claim 1 wherein calibrating further comprises fitting a linear curve to calibrate all sensor distances corresponding to each depth of field.

7. The method of claim 1 wherein calibrating further comprises calculating the second distance between the first nodal point and the second nodal point using a distance of an object, a calibrated quantity and a calculated quantity.

8. The method of claim 7 wherein calibrating further comprises calculating additional second distances and taking an average of the second distances calculated and generating a final result.

9. A system comprising:

a. a lens;

b. an image sensor configured for acquiring an image; and

c. a processor configured for calibrating the system using a first distance between a second nodal point and the image sensor, and calibrating the system using a second distance between a first nodal point and the second nodal point, wherein calibrating the system includes moving the lens based on the second nodal point and the image sensor, wherein calibrating further comprises utilizing a distance relationship, where there is a same object position but different lens settings, wherein calibrating further comprises utilizing a magnification factor, a distance to an object, and calibration information, wherein the magnification factor is calculated using a checkerboard object at a certain distance and taking pictures with the different lens settings, and the magnification factor is calculated by measuring distances between circle centers in the checkerboard object, wherein measuring the distances between the circle centers includes cropping out a patch that contains a circle, the patch is convolved with itself, a position of the maximal convolution result is determined, and a distance between the circle centers is measured.

10. The system of claim 9 wherein the calibrating further comprises taking a picture of a checkerboard pattern.

11. The system of claim 9 wherein the calibrating further comprises calculating a magnification factor by measuring a first distance of two corner points on a real checkerboard and a second distance of two corner points on an image of the checkerboard.

12. The system of claim 11 wherein corner detection is used to locate rough position of the corner points.

13. The system of claim 11 wherein calibrating further comprises calculating the first distance between the second nodal point and the image sensor using the magnification factor.

14. The system of claim 9 wherein calibrating further comprises fitting a linear curve to calibrate all sensor distances corresponding to each depth of field.

15. The system of claim 9 wherein calibrating further comprises calculating the second distance between the first nodal point and the second nodal point using a distance of an object, a calibrated quantity and a calculated quantity.

16. The system of claim 15 wherein calibrating further comprises calculating additional second distances and taking an average of the second distances calculated and generating a final result.

17. A camera device comprising:

a. a lens;

b. a sensor configured for acquiring an image;

c. a non-transitory memory for storing an application, the application for;

i. calibrating the camera device using a first distance between a second nodal point and the image sensor; and

ii. calibrating the camera device using a second distance between a first nodal point and the second nodal point, wherein calibrating the camera device includes moving the lens based on the second nodal point and the image sensor, wherein calibrating further comprises utilizing a distance relationship, where there is a same object position but different lens settings, wherein calibrating further comprises utilizing a magnification factor, a distance to an object, and calibration information, wherein the magnification factor is calculated using a checkerboard object at a certain distance and taking pictures with the different lens settings, and the magnification factor is calculated by measuring distances between circle centers in the checkerboard object, wherein measuring the distances between the circle centers includes cropping out a patch that contains a circle, the patch is convolved with itself, a position of the maximal convolution result is determined, and a distance between the circle centers is measured; and

d. a processor coupled to the memory, the processor configured for processing the application.

18. The camera device of claim 17 wherein the calibrating further comprises taking a picture of a checkerboard pattern.

19. The camera device of claim 17 wherein the calibrating further comprises calculating a magnification factor by measuring a first distance of two corner points on a real checkerboard and a second distance of two corner points on an image of the checkerboard.

20. The camera device of claim 19 wherein corner detection is used to locate rough position of the corner points.

21. The camera device of claim 19 wherein calibrating further comprises calculating the first distance between the second nodal point and the image sensor using the magnification factor.

22. The camera device of claim 17 wherein calibrating further comprises fitting a linear curve to calibrate all sensor distances corresponding to each depth of field.

23. The camera device of claim 17 wherein calibrating further comprises calculating the second distance between the first nodal point and the second nodal point using a distance of an object, a calibrated quantity and a calculated quantity.

24. The camera device of claim 23 wherein calibrating further comprises calculating additional second distances and taking an average of the second distances calculated and generating a final result.