Alleviating Radial Distortion Effect for Accurate, Iterative Camera Calibration Using Principal Lines

Preparing appropriate images for camera calibration is crucial to accurate calibration results. In this article, guidelines for preparing such data to alleviate the effect of radial distortion for accurate calibration procedure, using principal lines (PLs), are developed through 1) identifying directions of movement of calibration checkerboard (CB) pattern in an image which will result in maximum influence (deflection of the PL) on the calibration results and 2) inspecting symmetry and monotonicity of such adverse effect in 1). Accordingly, it is suggested that an iterative estimation of principal point (PP) with the above calibration procedure is based on linearly independent pairs of nearly parallel PLs, with one member in each pair corresponding to a 180° rotation (in the image plane) of the other. Experimental results on synthetic data show that more accurate (and robust) calibration can be achieved with the foregoing iterative approach using PLs compared with a similar implementation using the renowned algebraic (Zhang’s) method which explicitly estimates distortion parameters in the calibration. Moreover, similar results are obtained for real data via cross-validation of different sets of calibrated intrinsic/extrinsic camera parameters using reprojection errors, and from the consistency of flow vector field of camera distortion associated with different sets of intrinsic parameters.