A dark and light color separation of four fundamental colors into color materials containing light ink is realized at high speeds. A cross patch where a discrete color material amount with regard to two kinds of color materials having a different density is distributed in a cross pattern is printed by an image output device. In addition, there are produced a density characteristics map and a color material amount characteristics map. Accordingly, the cell of the equal color material amount is searched within a range not exceeding a target color material use amount from the color material characteristics map and the cell of the equal density is searched within a range not exceeding a target density from the density characteristics map. As a result, it is possible to determine a combination of a color material amount of each of a dark color material and a light color material.