An Evaluation of Color Aberration caused by the Optical Dot Gain

One of the issues relating to the four-color process prints is the optical dot gain caused by light penetration into the paper substrate. Neugebauer's Equation is well known for describing the color reproduction by halftone dots, but it is a little complicated. By assuming that the optical densities may be added to superimposed solid portions, Neugebauer's Equation can be resolved into factors which correspond to primary, secondary and tertiary colors of the respective inks and can be transformed into Pollak's Equation shown below. R4pollak = Rpp(1 - c + cRscp ) (1 - m + mRsmp ) (1- y + yRsyp ) (1- k + kRskp ) R4pollak : Reflectance, c,m y,k : dot values, Rpp: Reflection value of white portion, R sip: Reflectance value of solid portion for i ink When discussing the color reproduction, these factors affected by the optical dot gain should be examined. In this paper, definition of the optical dot gain is the difference between the measured reflectance values and the values calculated by Murray-Davies's Equation, and show that the optical dot gain can be estimated by the quadratic equation of the dot values.