Depth from physics: physics-based image analysis and feature definition

Blood vessels overlying one another at distinct depths (and hence appearing to intersect) in the conjunctiva of the eye can be distinguished reliably from those that in fact do branch within the same depth, using only the information contained in a single photograph of the conjunctiva. That conclusion arises from extension of earlier work that qualitatively inferred relative depth of vessels. The current research was motivated by the need to quantify such inferences in terms of their sensitivities and robustness. Features extracted from an image are shown to be useful in that effort; their utility is verified with phantoms that mimic the behavior of the conjunctiva and the backing sclera. Because no special preparations are needed, the method works as well on archived images as on newly-acquired ones, and thus can be used in retrospective studies of images of the eye and other diffuse media.