On the silhouette cartoon animation

This research addresses the issue of human visual cognitive capability to identify an object irrespective of object orientation throughout the course of object movement in computer animation. The identification is by cognizing the shape characteristics that are independent of the object orientation as invariants. Taking a simple case of a silhouette cartoon animation and having a dolphin as a popular example of an object that changes the orientation while swimming and also jumping up into the air, we show that the orientation independent invariants are the critical points, namely the peaks of the convex portion of the object and the pits of concave portions, and that they are derived from a graph of the curvature change along the boundary of the object.