Combining improved two-step method with virtual stereo pattern for stereo camera calibration

Camera calibration is a necessary step in computer vision. We presented a high-accurate technique for stereo camera calibration, which was realized by combining improved two-step method with virtual stereo calibration pattern, and considered radial distortion and tangential distortion. The most calibration parameters were estimated using a linear solution based on a pinhole camera model, we used the calibration points near the center of the image because of their little distortion for the solutions in the first step. In the second step, we took into account camera distortions and used all calibration points, the parameters estimated in the first step were improved iteratively through a nonlinear optimization. An infrared LED, which moved with three-dimensional coordinate measurement machine at certain distance, formed a virtual stereo pattern and given accurate calibration points. Using the calibration parameters computed by this technique to reconstruct calibration points, the accuracy is improved 0.11 mm compared with direct linear estimation.