Classical studies of measuring image motion by computer have concentrated on the case of optical flow , in which there is a unique velocity near each point of the image. In [5], we introduced a generalization of optical flow in which a range of parallel velocities can occur near each point in the image. Such image motion arises in many natural situations, such as camera motion in a cluttered 3-D scene or a stationary camera viewing falling snow. We refer to these image motions as optical snow. In the present paper, we show how the aperture problem manifests itself in this type of image motion.