CAMERA CALIBRATION FOR FISH-EYE LENSES IN ENDOSCOPYWITH AN APPLICATION TO 3D RECONSTRUCTION

Image analysis tasks such as 3D reconstruction from endoscopic images require compensation of geometric distortions introduced by the lens system. Appropriate camera calibration is thus necessary. Commonly used calibration algorithms rely on the well-known pinhole camera model, extended by parametric terms for radial distortions. In this paper, we demonstrate that these models are not appropriate if very strong distortions occur as is the case for endoscopic fish-eye lenses. As an alternative, we analyze a generic calibration algorithm published recently by Kannala and Brandt, which is based on more general projection equations. We show qualitatively and quantitatively that this algorithm is well suited to deal with significant distortions especially in the image's rim regions. Furthermore, we demonstrate how images of a colon phantom that were corrected in such a manner can be used to obtain a 3D reconstruction