Process control sensing of toner coverage

A toner coverage sensing system for sensing toner particles printed onto a surface of a process element using an electrophotographic printing system, the printed toner particles including printed porous color toner particles, comprising:

• an optical sensing system including:
• an infrared radiation source that directs infrared radiation in an infrared wavelength band onto the printed toner particles on the surface of the process element;
• and
• a diffused radiation detector for sensing infrared radiation scattered from the printed porous color toner particles on the surface of the process element, wherein the diffused radiation detector is oriented such that the sensed infrared radiation does not include specular reflections from the surface of the process element;
• and
• a data processing system that determines a sensed toner coverage for the porous color toner particles on the surface of the process element responsive to the sensed scattered infrared radiation;
• wherein the porous color toner particles absorb less than 5% of the radiation in the infrared wavelength band.