Subtractive Color Mixture and Color Reproduction*

The colors of mixtures of certain sets of dyes can be predicted to a close approximation through the use of a simple rule. The analytical form of this rule is sufficiently simple to permit its incorporation into the theory of color reproduction. This inclusion of the phenomena of subtractive mixture in the theory leads directly to the conclusion that masking is an essential step in any realizable subtractive process of correct color reproduction. Formulas for the calculation of the gradients of the masks are given in terms of the parameters of the rule for the prediction of the colors of mixtures of the dyes to be used in printing the subtractive reproduction. Formulas are also given for the calculation of the gradients of masks to be used for the simultaneous introduction of partially negative spectral sensitivities. An application of these formulas to the Eastman wash-off relief process shows that the negative portions of the theoretically desirable spectral sensitivities are negligible, and that each separation negative need be printed in register with only one mask.