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6.5 Exercises 301

Ex 6.11: Radial distortion with a calibration target Use a grid calibration target to de-
termine the radial distortion parameters.
1. Print out a planar calibration target, mount it on a stiff board, and get it to fill your field
of view.

2. Detect the squares, lines, or dots in your calibration target.
3. Estimate the homography mapping the target to the camera from the central portion of
the image that does not have any radial distortion.

4. Predict the positions of the remaining targets and use the differences between the ob-
served and predicted positions to estimate the radial distortion.

5. (Optional) Fit a general spline model (for severe distortion) instead of the quartic dis-
tortion model.

6. (Optional) Extend your technique to calibrate a fisheye lens.

Ex 6.12: Chromatic aberration Use the radial distortion estimates for each color channel
computed in the previous exercise to clean up wide-angle lens images by warping all of the
channels into alignment. (Optional) Straighten out the images at the same time.
Can you think of any reasons why this warping strategy may not always work?