A printing system is linearized automatically using measurements made with a simple optical sensor, such as a line sensor, that is onboard the system. The printing system itself is for forming images on plural printing media. Because the optical sensor is not a calorimeter or even a true densitometer, the sensor requires calibration, preferably based upon measurements using real inks. In the past it has been considered a requirement that such calibration be performed separately using each of the print media that was to be used for printing images. Linearization according to the invention, however, refers to a single calibration of the sensor, that calibration being used in common for essentially all media—even though the single calibration is performed with respect to exclusively a single one of the plural media.