From local to global parameter estimation in panoramic photographic reconstruction

This paper addresses a key issue in the problem of reconstructing a panoramic view from several pictures taken with a hand-held camera, namely the estimation of some ill-posed parameters using an external constraint. For many practical reasons, a panoramic reconstruction has to be performed in several independent steps, resulting in a set of different measurements of the same reality. For example, the focal length can be estimated with each pair of overlapping images. The idea is to introduce some a priori knowledge about the world by means of a constraint on the parameter set. In the former example, the constraint would impose equality on all the focal length estimates. This paper describes the appropriate correction that needs to be applied to the parameters in order to obtain a coherent result. It also suggests a way to evaluate if a constraint is plausible given a set of initial estimates. The basic idea behind the method is to modify the parameters without significantly changing the overlapping part of the images. The method is evaluated using two different experimental setups. The first aims at improving the quality of a full panoramic image. The second measures independently the positions in space of two planes using two pictures. The latter experiment shows that the two computed motions can be considered as a single one with two different planes in space.