Detecting Irregularities in Cyclic Motion

Real cyclic motions tend not to be perfectly even, i.e., the period varies slightly from one cycle to the next, because of physically important changes in the scene. A generalization of period is de ned for cyclic motions that makes periodic variation explicit. This representation, called the period trace, is compact and purely temporal, describing the evolution of an object or scene without reference to spatial quantities such as position or velocity. By delimiting cycles and identifying correspondences across cycles, the period trace provides a means of temporally registering a cyclic motion. In addition, several purely temporal motion features are derived, relating to the nature and location of irregularities. Results are presented using real image sequences and applications to athletic and medical motion analysis are discussed.