Light is obliquely irradiated onto the surface of a document in braille, and its reflected light is received, to obtain a first gray image. The first gray image is subjected, while being scanned in a direction corresponding to a direction parallel to the direction of light irradiation, to differentiation...http://www.google.de/patents/US5920649?utm_source=gb-gplus-sharePatent US5920649 - Braille recognition system with ternary-coding
