Self-calibration with varying focal length from two images obtained by a camera with small rotation and general translation

The stratified self-calibration approach based on the absolute conic or its dual, the absolute dual quadric, has the merit of allowing the intrinsic camera parameters to vary while being retrieved from an image sequence. In this paper, we show that for a camera with small rotation and general translation, a new linear equation resulted from the infinity homography can be added to a system of linear equations to compute the absolute dual quadric. Experiments with both synthetic and real images show that satisfactory results can be obtained with the proposed linear approach. It is possible to further improve the calibration result by adopting some nonlinear optimization schemes, e.g., a suitable LM-like algorithm, to enforce the absolute dual quadric constraints using the linear solutions as an initial guess. (C) 2001 Elsevier Science B.V. All rights reserved.