Using Sphere Images for Calibrating Fisheye Cameras under the Unified Imaging Model of the Central Catadioptric and Fisheye Cameras

This paper proposes a novel calibration method for fisheye cameras using sphere images which is an extension of the calibration method for central catadioptric cameras. We show that, each sphere image under fisheye cameras is tangent to the modified calibrating conic (MCC) at two double-contact image points. The calibration method is proposed by first finding the double-contact image points, then fitting the MCC, and final obtaining the intrinsic parameters using the LDLT factorization of the MCC.