Is it really necessary to use spectrophotometry to control the ink keys?
In order to answer this question it is important to clarify a few terms used in color science and analyze their relevance for printing ink-control. Densitometers, Colorimeters and Spectrophotometers, measure light intensities through a set of colored filters or diffraction elements. There are two differences between these three devices: • Number of filters (= “channels”) used • Output data: only density or density + color definition (e.g. L*A*B*, or equivalent) Densitometers and Colorimeters usually use 3 to 6 filters. Using their filters the Densitometers recognize the color of the examined patch (CMYK). Thus Densitometers give density information for each CMYK patch: how much light is absorbed by ink coverage on top of the paper. This is proportional to ink thickness above the sheet. As the thickness of the ink is controlled by and only by three elements: the ink keys, the water-ink balance and the ink-roller speed – monitoring density changes is the only information needed. Colorime
