Real time edge extraction by active defocusing

A novel edge extraction method that employs an active defocusing technique is presented. The method is based on the principle that a Laplacian of Gaussian (LOG) operator can be well approximated by a Difference of Gaussian (DOG) operation.. While such operation can be done by digital processing, it is more effective to be conducted in a combination of optical and digital processing techniques. In this edge extraction process, a focused image of object in scene is first acquired. Image of the scene is then slightly defocused by changing the focal length of camera lens. Real time subtraction is applied to the defocused and the previously acquired images. It produces a residual image that emphasizes abrupt intensity variations, which are typical of edges in the image. An objective evaluation called edge index is performed on the resulting image. Amount of defocusing is carefully adjusted according to this measurement so that a desired edge image is generated. Boundaries of objects can then be obtained by further enhancement of the edge image. Since this edge detection method is an optical-based process aided by digital processing, it is rather fast and less expansive.