As described above, in a case in which the first gradation value (0.5 in the above-described case) and the second gradation value (0.3 in the above-described case) smaller than the first gradation value are the characteristics-acquired gradation values, then in Step S150, regarding the process target gradation value between the maximum gradation value and the first gradation value, the equation that represents the relationship between the spectral reflectances of the maximum gradation value and the spectral reflectances of the process target gradation value with the spectral reflectances of the maximum gradation value being taken as the first reference and the spectral reflectances of the first gradation value being taken as the second reference is obtained as the second relational equation; regarding the process target gradation value between the first gradation value and the second gradation value, the equation that represents the relationship between the spectral reflectances of the first gradation value and the spectral reflectances of the process target gradation value with the spectral reflectances of the first gradation value being taken as the first reference and with the spectral reflectances of the second gradation value being taken as the second reference is obtained as the second relational equation; and regarding the process target gradation value between the second gradation value and the minimum gradation value, the equation that represents the relationship between the spectral reflectances of the second gradation value and the spectral reflectances of the process target gradation value with the spectral reflectances of the second gradation value being taken as the first reference and with the spectral reflectances of the minimum gradation value being taken as the second reference is obtained as the second relational equation.