Computations underlying the measurement of visual motion

Abstract

Abstract The organization of movement in a changing image provides a valuable source of information for analyzing the environment in terms of objects, their motion in space, and their three-dimensional structure. A description of this movement is not provided to our visual system directly, however; it must be inferred from the pattern of changing intensity that reaches the eye. This paper examines the problem of motion measurement, which we formulate as the computation of an instantaneous two-dimensional velocity field. Initial motion measurements occur at the location of significant intensity changes, as suggested by Marr and Ullman [1]. These measurements provide only one component of velocity, and must be integrated to compute the two-dimensional velocity field. A fundamental problem for this integration is that motion is not determined uniquely from the changing image. An additional constraint of smoothness of the velocity field is formulated, based on the physical assumption that surfaces are generally smooth, allowing the computation of a unique solution. A theoretical analysis of the conditions under which this computation yields the correct velocity field suggests that the solution is physically plausible; empirical studies show the results to be consistent with human motion perception.