An ink set that includes a plurality of chromatic primary color inks that can reproduce achromatic color in combination with each other and at least one spot color ink having a hue different from any of the chromatic primary color inks is prepared. A color to be reproduced on a printing medium in accordance with a given input color is termed a reproduction color, and a combination of ink amounts for inks in the ink set to be used to reproduce the reproduction color on the printing medium is termed a color separation ink amount set. When a saturation parameter value that is correlated with the saturation of the reproduction color falls within a first range that is close to achromaticity, the ink amount of the spot color ink included in the color separation ink amount set is adjusted such that it decreases in accordance with a change in the saturation parameter value in the direction of lower saturation.