Additivity of Ink Densities in Multicolor Halftone Printing.

The colors of any combination of printing inks depend on (1) the colors of the individual inks throughout the scale from white paper to solid ink; and (2) the additivity of the densities of the superimposed inks when measured through color filters. The former is easily determined; the latter is more complex because of the large numbers of possible combinations. Additivity behavior depends on the following factors: first-surface reflections, multiple internal reflections, trapping, back transfer, opacity of ink, spectral absorption characteristics of ink and paper, spectral sensitivity characteristics of the measuring instrument, halftone structure, and sideways scattering of light in the paper. The effect of most of these factors on additivity has been worked out theoretically, and actual measurements are in satisfactory agreement with the theoretical results.