Registration of white toner in an electrophotographic printer

An electrophotographic printing system for printing with a set of toners including a non-pigmented toner, comprising:

• (a) a transport web that is at least partially transparent, wherein the transport web moves in an in-track direction;
• (b) a plurality of printing modules, each printing module configured to print a toner pattern using a respective toner from the set of toners onto a first surface of the transport web, wherein the toner pattern includes a toner image to be printed onto a receiver medium being transported on the first surface of the transport web and a corresponding registration mark positioned outside a border of the receiver medium;
• (c) a first registration mark sensing system positioned to detect the registration marks printed with a first subset of the toners that doesn't include the non-pigmented toner, the first registration mark sensing system including:
• (i) a first light source positioned over the first surface of the transport web;
• (ii) a first reflector plate positioned behind the transport web, wherein the first reflector plate has a color which is lighter than the toners in the first subset of toners;
• and
• (iii) a first light detector positioned over the first surface of the transport web;
• wherein the first light detector is positioned to detect light that is emitted by the first light source, transmitted through the transport web and reflected off the first reflector plate;
• (d) a second registration mark sensing system positioned to detect the registration marks printed with a second subset of the toners that includes the non-pigmented toner, the second registration mark sensing system including:
• (i) a second light source positioned over the first surface of the transport web;
• (ii) a second reflector plate positioned behind the transport web, wherein the second reflector plate has a color which is darker than the non-pigmented toner;
• and
• (iii) a second light detector positioned over the first surface of the transport web;
• wherein the second light detector is positioned to detect light that is emitted by the second light source, transmitted through the transport web and reflected off the second reflector plate;
• and
• (e) a registration correction system that analyzes signals from the first and second registration mark sensing systems to detect positions of the registration marks printed by each of the printing modules, determines corresponding registration errors, and adjusts the registration of subsequently printed toner patterns to compensate for the determined registration errors.