Describing motion for recognition

Our goal is to describe motion of a moving human figure in order to recognize individuals by variation in the characteristics of the motion description. We begin with a short sequence of images of a moving figure, taken by a static camera, and derive dense optical flow data for the sequence. We determine a range of scale-independent features of each how image as a whole, ranging from the motion of the centroid of the moving points (assuming a static background), to the integral of the torque relative to the centroid. We then analyze the periodic structure of these sequences. All elements are multiples of the fundamental period of the gait, but they differ in phase. The phase is time-invariant, since it is independent of the sampling period. We show that there are several regularities in the phase differences of the signals. Moreover, some scalar measures of the signals may be useful in recognition. The representation is model-free, and therefore could be used to characterize the motion of other non-rigid bodies