Spectral Reflectance Prediction of Ink Overprints by Kulbeka-Munk Turbid Media Theory

An algorithm was tested for predicting the spectral reflectance factor of ink overprints, known as the Neugebauer primaries, using Kubelka-Munk turbid media theory. Two ink optical constants, spectral absorption and scattering coefficients, ink thickness, and the paper substrate's spectral reflectance factors are the key parameters to estimate the spectral reflectance factors of a translucent ink printed on top of an opaque support. This article shows the processes to determine the two optical constants and thickness, i.e., the characteristic parameters of an ink. Once all characteristic parameters of each ink are determined, the prediction of overprints is simply exercising the general form of the Kubelka-Munk equation. High colorimetric and spectral accuracy was obtained using this approach when predicting 100% overprints produced using the DuPont Water Proof proofing process.