One aspect of the invention comprises a method of embedding data in a code readable by machine from a visible light scan of the code. The method comprises pre-printing a two dimensional array of pixels on a substrate. The pixels include at least one calibration pixel, and each have color values. The...http://www.google.com.hk/patents/US7789311?utm_source=gb-gplus-share專利 US7789311 - Three dimensional data storage
