The requirements for a photographic system to reproduce the chromaticities of selected colors can be described by a set of equations. These equations relate the amounts of dye needed in the reproduction to the exposure densities of the original colors. These equations have been called color-reproduction equations by Brewer, Hanson, and Horton. These color-reproduction equations have been computed for a negative-positive color system.
The equations state the requirements placed on a color system if it is to reproduce the chromaticities of the original. A similar set of color-reproduction equations can be computed which describe the actual performance of the color system. These actual color-reproduction equations are established by measuring the actual amount of dye produced in a process when reproducing a color chart. These amounts of dye are related to the exposure densities of the original colors. The required and actual color-reproduction equations for a negative-positive color system are compared. The similarity between these sets of equations show how well a modern negative-positive color system fulfills conditions of good color reproduction.
W. R. J. BROWN, "Subtractive Color Reproduction: Evaluation of the Actual Color-Reproduction Equations for a Color Process," J. Opt. Soc. Am. 45, 539-541 (1955)