System for optically detecting and measuring release agent on a print drum in an ink jet printer

A system optically detects and measures release agent on a rotating image member in an ink jet printer. The system includes a collimated light source oriented to direct a collimated beam of light generated by the source towards a rotating image member, an image sensor for generating an image of a portion of the rotating image member from a portion of the collimated beam of light reflected by the rotating image member, an image differentiator for measuring a difference between a first image generated by the image sensor and a second image generated by the image sensor, and a release agent measurement generator that is coupled to the image differentiator to receive the difference between the two images and to generate a measurement of the release agent on the rotating image member.