Method for high precision lens distortion calibration and removal

• US 8,681,224 B2
• Filed: 06/26/2008
• Issued: 03/25/2014
• Est. Priority Date: 06/26/2007
• Status: Expired due to Fees

• Current Assignee: Dublin City University
• Original Assignee: Dublin City University
• Inventors: Mallon, John, Whelan, Paul F.
• Primary Examiner(s): Tran, Nhan T
• Assistant Examiner(s): Wang, Xi
• Application Number:
  US12/666,178
• Publication Number:
  US 20120057053A1
• Time in Patent Office: 2,098 Days
• Field of Search: 348/180, 348/187, 348/188, 348/222.1, 348/335, 348/241, 353/34, 356/124
• US Class Current: 348/187
• 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 5/006 Geometric correction correction of chromatic aberrations adapted to be used in an image pickup device containing an electronic image sensor H04N23/10; detecting, correcting, reducing or removing artefacts resulting only from the lens unit, e.g. flare, shading, vignetting or "cos4" H04N25/61
• 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:

capturing an image of a target with a known structure through the lens, the target comprising a known, two-dimensional, 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 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 an estimated location for distorted control points,

comparing these estimated locations to the Euclidean transformed detected control points while simultaneously refining 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.

2. A method according to claim 1, wherein the target includes a checkerboard pattern and the plurality of control points are the corners of the squares.

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

4. A method according to claim 3, further comprising scaling the captured image.

5. A method according to claim 4, wherein the degree of scaling is determined directly from the distortion model to minimize average pixel stretch throughout the image.

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

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

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

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

comparing these estimated points without distortion to the estimated positions of the control points without distortion obtained through projective transformation of their known structure and adjusting 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.

7. A method according to claim 6, wherein the target includes a checkerboard pattern and the plurality of control points are the corners of the squares.

8. A method according to claim 6, further comprising applying the distortion model with stored model parameters to correct a further captured image to produce an undistorted image.

9. A method according to claim 8, further comprising scaling the captured image.

10. A method according to claim 9, wherein the degree of scaling is determined directly from the distortion model to minimize average pixel stretch throughout the image.

11. 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, two-dimensional, planar structure comprising a plurality of control points;

detecting the positions of the plurality of control points in the captured image, transforming detected positions of the control points into a lens centric coordinate system using a Euclidean Transform and initial transformation values;

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

comparing and simultaneously refining 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 Euclidean transformed detected positions of the control points, and storing distortion model parameters once the difference has been minimized.

12. A method according to claim 11 wherein the target includes a checkerboard pattern and the plurality of control points are the corners of the squares.

13. A method according to claim 11, further comprising applying the distortion model with the stored model parameters to correct a further captured image to produce an undistorted image.

14. A method according to claim 13, further comprising scaling the captured image.

15. A method according to claim 14, wherein the degree of scaling is determined directly from the distortion model to minimize average pixel stretch throughout the image.

16. An imaging system comprising a lens and an imaging device, wherein the system is adapted to perform the method of claim 11.

17. An imaging system according to claim 16, wherein the imaging system is a camera and the imaging device is a sensor.

18. A camera according to claim 17, wherein the sensor is a CCD device.

19. An imaging system according to claim 18, wherein the imaging system is a projector.

20. A projector according to claim 19, wherein the imaging device is a LCD device.