Relief image scanner

Abstract

A relief image scanner scans successive linear areas on an information-carrying medium such as a plastic card, illuminating each area from two different directions. The reflected light is converted to first gray-level data when the illumination is from one direction, and to second gray-level data when the illumination is from the other direction. The second gray-level data are subtracted from the first gray-level data; then the difference, and its additive inverse, are compared with a threshold to detect edges of relief patterns on the card, and pairs of edges are connected to create an accurate, distortion-free image of the relief. Additional facilities may be provided to extract edge skeletons before joining the edges, and to capture printed information by binarizing the gray-level data.