A color data setting unit that sets a plurality of sets of fifth color data that are defined in a first color space in one to one correspondence with a plurality of fourth color data sets. An identifying unit identifies some of first reference points, that are in proximity to the fifth color data set for each of second reference points. A calculation unit calculates, for each of all the second reference points, color differences between the fifth color data set for the each second reference point and the some of the first reference points. A determining unit determines, for each of the first reference points, a single fifth color data set that has the smallest color difference among all the color differences that are calculated with respect to the each of the first reference points. A registering unit registers, at each of the first reference points, the fourth color data set that is set in correspondence with the single fifth color data sets.