METHOD FOR HIGH PRECISION LENS DISTORTION CALIBRATION AND REMOVAL

• US 20120057053A1
• Filed: 06/26/2008
• Published: 03/08/2012
• Est. Priority Date: 06/26/2007
• Status: Active Grant

• Current Assignee: Dublin City University
• Original Assignee: Airbus Operations (European Aeronautic Defence and Space Company EADS NV)
• Inventors: Mallon, John, Whelan, Paul F.
• Granted Patent: US 8,681,224 B2
• Time in Patent Office: Days
• US Class Current: 348/241
• 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
• CPC Class Codes: G06T 5/80 Geometric correction
• CPC Class Codes: H04N 25/61 the noise originating only from the lens unit, e.g. flare, shading, vignetting or "cos4"

Abstract

The present application relates to a high precision method for calibrating and removing distortion from a lens, and more particularly, a method for calibrating and removing distortion by arranging sensor readings to compensate for its presence and simultaneously optimize the resulting image magnification for best image quality.

Claims

1. A method for determining lens distortion parameters for an imaging system comprising a lens and an imaging device, the method comprising the steps of:

capturing an image of a target with a known structure through the lens, the target comprising a known planar structure comprising a plurality of control points;

detecting the positions of the plurality of control points in the captured image,

performing a Euclidean transform on the detected control points,

calculating an estimate for the positions of the control points without distortion through a projective transformation of their known structure in conjunction with a distortion model applied to these estimated control points to provide a estimated location for the distorted control points,

comparing these estimated locations to the Euclidian transformed detected control points while simultaneously refining the estimated positions through the projective transformation, the distortion model and the Euclidean transform of the measured control point coordinated, to minimize the difference, and

storing the distortion model once the difference has been minimized.

14. A method according to claim 1, further comprising the step of applying the distortion model with the stored model parameters to correct a further captured image to produce an undistorted image.

15. A method according to claim 14, further comprising the step of scaling the captured image.

16. A method according to claim 15, wherein the degree of scaling is determined directly from the distortion model to minimize the average pixel stretch throughout the image.

17. A method according to claim 1, wherein the test pattern is a checkerboard pattern and the test points are the corners of the squares.

2-13. -13. (canceled)

18. A method for determining lens distortion parameters for an imaging system comprising a lens and an imaging device, the method comprising the steps of:

capturing an image of a target with a known structure through the lens, the target comprising a known planar structure comprising a plurality of control points;

detecting the positions of the plurality of control points in the captured image,

estimating positions of the detected control points without distortion by applying a Euclidian transform to the detected values in conjunction with a distortion model applied to the Euclidian transformed detected values,

comparing these estimated points without distortion to the estimated positions of the control points without distortion obtained through the projective transformation of their known structure and adjusting the parameters of the distortion model, Euclidean transform and estimated values to minimize the difference, and

storing the distortion model once the difference has been minimized.

19. A method according to claim 18, further comprising the step of applying the distortion model with the stored model parameters to correct a further captured image to produce an undistorted image.

20. A method according to claim 19, further comprising the step of scaling the captured image.

21. A method according to claim 20, wherein the degree of scaling is determined directly from the distortion model to minimize the average pixel stretch throughout the image.

22. A method according to claim 18, wherein the test pattern is a checkerboard pattern and the test points are the corners of the squares.

23. A method for determining lens distortion parameters for an imaging system comprising an imaging device and lens, the method comprising:

capturing an image of a target through the lens, the target comprising a known planar structure comprising a plurality of control points;

detecting the positions of the plurality of control points in the captured image,

transforming the detected positions of the control points into a lens centric co-ordinate system using initial transformation values,

computing an estimate for the positions of the control points without distortion in conjunction with a distortion model applied to the estimated control points to provide a estimated location for the distorted control points, and

comparing and simultaneously refining the estimated positions, the parameters of the distortion model and the initial transformation values to minimize the difference between the estimated positions of the control points and the transformed detected positions of the control points, and

storing the distortion model parameters once the difference has been minimized.

24. A method according to claim 23, further comprising the step of applying the distortion model with the stored model parameters to correct a further captured image to produce an undistorted image.

25. A method according to claim 24, further comprising the step of scaling the captured image.

26. A method according to claim 25, wherein the degree of scaling is determined directly from the distortion model to minimize the average pixel stretch throughout the image.

27. A method according to claim 23 wherein the test pattern is a checkerboard pattern and the test points are the corners of the squares.

28. An imaging system comprising a lens and an imaging device, wherein the system is adapted to perform the method of claim 23.

29. An imaging system according to claim 28, wherein the imaging system is a camera imaging device is a sensor.

30. A camera according to claim 29, wherein the sensor is a CCD device.

31. An imaging system according to claim 30, wherein the imaging system is a projector.

32. A projector according to claim 31, wherein the imaging device is a LCD device.