Finally, the prediction values of the spectral reflectances of the gradation value which is not included in the union among the plurality of gradation values serving as the prediction target gradation values are obtained by spline interpolation based on the prediction values obtained in Step S280 (Step S290). If eleven gradation values in increments of 0.1 from the gradation value of 0 to the gradation value of 1 are the prediction target gradation values, then in the example illustrated in FIG. 16, the prediction values of the spectral reflectances of the gradation values of 0.1, 0.4, 0.6, 0.7, and 0.9 for the prediction target color are obtained by this Step S280. At this time, the spine interpolation is performed using the prediction values (prediction values obtained in Step S280) of the spectral reflectances of at least three gradation values among the gradation values of 0, 0.2, 0.3, 0.5, 0.8, and 1. Note that, though linear interpolation can also be used in place of the spline interpolation, the prediction values are obtained more accurately by the spline interpolation than the linear interpolation. Incidentally in a case in which all the plurality of gradation values as the prediction target gradation values are included in the union, the spectral reflectances of all the prediction target gradation values for the prediction target color have been obtained at the point of time when Step S280 is ended, and accordingly, there are no spectral reflectances obtained in Step S290.

In such a way as described above, the prediction values of the spectral reflectances of the prediction target gradation value for the prediction target color are obtained. Thus, the spectral reflectances prediction process is ended.