New perspectives on optical flow

摘要

The concept of optical flow originated in the study of moving vision, as a means of describing the instantaneous motion of images in the visual field of an observer resulting from relative motion of the observer and objects in the outside world. Work in this area has hitherto been based on the assumption that light travels in straight lines from object to observer. If, however, the refractive index of the medium between object and observer is nonuniform, light rays will bend according to Snell's law of refraction; under such conditions the motion field will be distorted. Furthermore, a time-dependent refractive index profile will result in image motion even when there is no relative motion between object and observer. This suggests a need for a broader definition of what constitutes optical flow. A very different phenomenon, but one which again involves image motion, is the motion of interference fringes in interferometry. Here also, optical flow would be a potentially useful way of describing the image motion. A simple example is given of an interferometry set-up where the optical flow is directly related to a changing physical parameter. Hence it would appear that the optical flow concept can be applied to a range of phenomena which involve moving images. A general framework to encompass the various forms of optical flow is presented.