An optical scanning and encoding device for providing a print signal pulse train to an ink jet printer in which a master image, including a reference image area, is scanned along a scan line. An optical scanner scans the master image and provides a signal which is inversely related to the print density...http://www.google.com.au/patents/US4151555?utm_source=gb-gplus-sharePatent US4151555 - Optical scanning and encoding device
