Front and back printing on security document substrates

Techniques are described for printing on front and back surfaces of security document substrates in a manner that conserves use of print ribbon, thereby extending the life of the print ribbon. In general, the printer controller knows the content, as well as locations and colors, of what has been printed on the front or first surface of the security document substrate. The printer control also knows the content, as well as locations and colors, of what is to be printed on the back or second surface of the security document substrate. When the back surface of the substrate is to be printed, the printer controller determines, for a particular color, whether any of the printing on the back surface would overlap with the printing on the front surface. For locations where there would be no overlap, the printer can reuse the section of print ribbon that was used to print on the front surface to print on the back surface.