Patent ID: 8427697

Claim:
A color separation method for determining amounts of a plurality of color inks in order to reproduce an arbitrary color with the plurality of color inks on a printing medium, the method comprising the steps of: (a) defining an ink set that includes as useable inks a plurality of chromatic primary color inks that when used in combination can reproduce achromatic color, and at least one spot color ink of hue different from any of the plurality of chromatic primary color inks, wherein a color component of the spot color ink can be separated into two color components of the chromatic primary color ink; (b) determining a plurality of reproduction colors to be reproduced on a print medium according to a plurality of input colors within a chromatic primary color space, a term “reproduction color” denoting a color to be reproduced on the print medium according to any one input color, a term “color separation ink amount set” denoting a combination of ink amounts of the ink set for reproducing a reproduction color on the print medium, a term “chromatic primary color space” denoting a color space having base vectors representing ink amounts of the plurality of chromatic primary color inks; and (c) determining a plurality of color separation ink amount sets for reproducing the plurality of reproduction colors, wherein the step (c) includes, for each reproduction color, the steps of: (c1) calculating a color saturation parameter value correlated to saturation of the reproduction color; and (c2) adjusting an ink amount of the spot color ink in the color separation ink amount set for the reproduction color such that the ink amount of the spot color ink decreases as the saturation parameter value changes in a direction of lower saturation when the color saturation parameter value falls within a prescribed first low-saturation range that is close to achromaticity.