A Practical Estimating Method of Camera´s Focal Length and Extrinsic Parameters from a Planar Calibration Image

The paper presents a new closed-form solution to estimate focal length and extrinsic parameters from a single calibration image. Firstly, a new backward camera model which is based on plane equation of calibration panel in 3D space is introduced, and three indirect extrinsic parameters are used to determine the final extrinsic parameter. Based on this model and distance between neighboring control points in calibration panel, the focal length and indirect extrinsic parameters are compute with closed-form solution and numerical post-processing. The estimated results of simulated camera and actual camera show that our method has higher accuracy and less computational complexity. The method can be used for on-line camera self-calibration where relative low calibration accuracy can be accepted and low algorithm complexity is needed, or as the initial values of complex optimization algorithm.