Efficient generic calibration method for general cameras with single centre of projection

Generic camera calibration is a non-parametric calibration technique that is applicable to any type of vision sensor. However, the standard generic calibration method was developed such that both central and non-central cameras can be calibrated within the same framework. Consequently, existing parametric calibration techniques cannot be applied for the common case of cameras with a single centre of projection (e.g. pinhole, fisheye, hyperboloidal catadioptric). This paper proposes improvements to the standard generic calibration method for central cameras that reduce its complexity, and improve its accuracy and robustness. Improvements are achieved by taking advantage of the geometric constraints resulting from a single centre of projection in order to enable the application of established pinhole calibration techniques. Input data for the algorithm is acquired using active grids, the performance of which is characterised. A novel linear estimation stage is proposed that enables a well established pinhole calibration technique to be used to estimate the camera centre and initial grid poses. The proposed solution is shown to be more accurate than the linear estimation stage of the standard method. A linear alternative to the existing polynomial method for estimating the pose of additional grids used in the calibration is demonstrated and evaluated. Distortion correction experiments are conducted with real data for both an omnidirectional camera and a fisheye camera using the standard and proposed methods. Motion reconstruction experiments are also undertaken for the omnidirectional camera. Results show the accuracy and robustness of the proposed method to be improved over those of the standard method.