A dot angle conversion unit 21 converts the dot angle of image data in an image area, separated by a boundary tracing unit 12, into 0 degree or 45 degrees. An in-mark correlation checking unit 22 determines a dot frequency of the image data whose dot angle has been converted. A mark re-dividing unit...http://www.google.de/patents/US6526172?utm_source=gb-gplus-sharePatent US6526172 - Coding method and coder using pattern matching
