1. A method of calibrating an image sensing system, the method comprising the steps of: sensing, by a photoelectric sensor, a first set of tone patches having first known densities and outputting first sensed density values; generating a first tone reproduction curve based on the first sensed density values and the first known densities, the first tone reproduction curve providing corrected density values for corresponding sensed density values output by the photoelectric sensor; storing the first tone reproduction curve in a storage device; sensing, by the photoelectric sensor, a second set of tone patches having second known densities and outputting second sensed density values, the second set of tone patches being sensed at a time subsequent to a time when the first set of tone patches was sensed; and calibrating the first tone reproduction curve to generate a second tone reproduction curve that is a calibrated tone reproduction curve based on the first tone reproduction curve, the second sensed density values, and the second known densities.