Calibration of stereo cameras using a non-linear distortion model [CCD sensory]

A camera model is presented which accounts for major sources of camera distortion: radial, decentering, and thin-prism distortions. The proposed calibration procedure consists of two steps. In the first step, calibration parameters are estimated using a closed-form solution based on a distortion-free camera model. In the second step, the parameters estimated in the first step are improved iteratively through nonlinear optimization, taking into account camera distortions. According to minimum-variance estimation, the objective function to be minimized is the mean-square discrepancy between the observed image points and their inferred image projections computed with the estimated calibration parameters. A type of measure is introduced which can be used to directly evaluate the performance of the calibration and compare calibrations among different systems. The validity and the performance of the calibration procedure are tested on real images taken by wide-angle lenses. Results consistently show significant improvements over less complete camera models