The history of three-color photography (1925)

Historical and Theoretical Data 33 He pointed out that Maxwell's curves were derived by adding three monochromatic lights, and are only true of such colors. All colors, including white, can be matched in hue and luminosity by combining the three fundamental colors as lights. Theoretically it is possible to do the same with printing inks, but the result would be a very dark picture of no practical use, as it would have to be examined in full sunlight. There is a fundamental difference in mixing colored lights and colored pigments. In the first case, if two filters transmit a common color, the result on the screen is a doubling of the amount of the common color. But in printing, if a spectrum color is completely absorbed by one ink, and is also absorbed by another, the total light absorbed by superposition is not twice that removed by the single ink. The law is a geometrical and not an arithmetical one, and if two inks separately transmit one-tenth of the light, the two together would not transmit one-twentieth, but only one-hundredth. This is of extreme importance in "process" work, for there the inks are always printed full strength, and the tint is regulated by the Percentage tenspasency of BOuelnk. size of the dots, that is by the percentage area of the paper covered by the ink. Each color is produced by similar dots, and when the three inks are printed, these dots partly overlap one another. As the dots are very closely spaced it is impossible in ordinary commercial printing to control the extent of the overlap; that is to say, the successive impressions will, owing to minute differences in "registering" the paper, have the dots of the different colors more or less displaced in relation to each other. If, for instance, the blue dots and the pink dots happened each to exactly cover half the area, in one impression they might be exactly superimposed, and in another