A piecewise affine model for image registration in nonrigid motion analysis

A piecewise-affine image registration method is proposed to compute the displacement field in an image sequence of an aerodynamic object experiencing heavy winds in a wind tunnel. Our method is useful for tracking objects whose net 3-D motion is fully characterized by a non-rigid motion and a significant component that is common to all parts of the object. A set of control points has been introduced on the object surface to help divide each image into a set of triangles and enable tracking each triangular area. The computed velocity field is piecewise affine for each triangle and is continuous across the boundary between any two adjacent triangles. Of interest is the accuracy of the registration process, and its estimate based on local moments and shape distortion that can be computed from the original image and the motion compensated version of its registered pair. The method has been applied to several images and the experimental results are presented