Recovery of nonrigid motion and structure

Abstract

Previous work on motion has almost uniformly relied on the rigid-body assumption, which is motivated by the need to estimate a limited number of parameters. Nonrigid motion, however, is both common and difficult to deal with by means of rigid-body schemes. We introduce a model of nonrigid motion that is based on the finite-element method and which produces accurate, overconstrained estimates of both rigid and nonrigid motion by means of a simple linear-regression technique. This method is based on the realization that the intrinsic elastic properties of real materials imply that nonrigid motion is not completely unstructured; rather, it has limited variability and may be accurately described by a small number of easily estimated parameters. Several examples using gray-scale and x-ray imagery are presented.