An instrument used to measure the ink density of printed products and the degree of blackening of negative or positive films and bromides in photography. A densitometer can also be used to determine the density of profiles. Densitometers measure a color sample three times using three different color filters (red, green and blue filters), which are equivalent to the sensitivity of the three types of cones in the human eye, and densitometers are thus also referred to as three-filter reading devices.