Spectral Based Ink Selection for Multiple-Ink Printing II. Optimal Ink Selection

An algorithm is described to select a set of six inks from a given ink database for a spectral-based six-color printing system which minimizes metamerism. Since there are C(n, 6) ink combinations for an ink database containing n inks, the number of ink combinations is a geometric figure when n is large. There are obviously impossible ink combinations which can be removed analytically. Vector correlation analysis is first employed to remove the infeasible combinations. Utilizing the statistical primaries of a given spectral image requiring reproduction as the basis information, the ink-selection algorithm then searches for similar inks through a given ink database to obtain a few highest correlated inks for each statistical primary. Second, the ink-selection algorithm estimates the colorimetric and spectral accuracy of candidate ink sets in an empirically derived color mixing space which approximates the color formation of a halftone printing process. The candidate ink set with the highest spectral accuracy will be designated as the optimal ink set for a six color printing process thereby achieving the least metameric color reproduction.