US Patent 8469482 Method for determining variance of inkjet sensor

A method for determining a variance of a sensor in inkjet printers includes maintaining a printer carriage at a stationary position; illuminating a media patch of known characteristics with a light source that varies an intensity of the light between at least a first and second intensity, in which the second intensity is different from the first intensity; obtaining at least specular reflectance data from light reflected off the print media by measuring a signal from a photo-detector during the illumination; and comparing the specular data to stored values to determine a variation of the sensor response for forming a correction factor; and using the correction factor to calibrate at least a first signal of the inkjet printer.