Apparatus and method for storing large amount of digital data into the color halftone micro-dots generated by high resolution color laser or ink jet printers or lithography on a substrate, such as paper. A data cell composed of color halftone micro-dots is encoded with multi-bit digital binary...http://www.google.de/patents/US5818032?utm_source=gb-gplus-sharePatent US5818032 - Encoded color halftone micro-dots for high density digital information storage 
