Next, with a maximum gradation value or a characteristics-acquired gradation value being taken as a reference gradation value, the second relational equation which represents the relationship between the spectral reflectances of the reference gradation value and the spectral reflectances of the above-mentioned process target gradation value for the reference color is obtained by the method similar to that in the above-described second embodiment (Step S270). Note that, in the present embodiment, the gradation values included in the union will be the process target gradation values. In the example illustrated in FIG. 16, the second relational equations corresponding to the gradation values of 0, 0.2, 0.3, 0.5, 0.8, and 1 are obtained by this Step S270. In this regard, for example, the second relational equation corresponding to the gradation value of 0.2 represents a relationship between the spectral reflectances of the gradation value of 0.3 and the spectral reflectances of the gradation value of 0.2 with the spectral reflectances of the gradation value of 0.3 being taken as a first reference and with the spectral reflectances of the gradation value of 0 being taken as a second reference. Moreover, for example, the second relational equation corresponding to the gradation value of 0.8 represents a relationship between the spectral reflectances of the gradation value of 1 and the spectral reflectances of the gradation value of 0.8 with the spectral reflectances of the gradation value of 1 being taken as a first reference and with the spectral reflectances of the gradation value of 0.5 being taken as a second reference.
