As described above, in a case in which the number of characteristics-acquired gradation values is one, then in Step S150, regarding the process target gradation value between the maximum gradation value and the characteristics-acquired 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 with the spectral reflectances of the characteristics-acquired gradation value being taken as the second reference is obtained as the second relational equation; and regarding the process target gradation value between the characteristics-acquired gradation value and the minimum gradation value, the equation that represents the relationship between the spectral reflectances of the characteristics-acquired gradation value and the spectral reflectances of the process target gradation value with the spectral reflectances of the characteristics-acquired 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.
In the above-described example, only the gradation value of 0.5 is the characteristics-acquired gradation value. That is, the number of characteristics-acquired gradation values is one. In a case in which the number of characteristics-acquired gradation values is 2 or more, the second relational equation is obtained as follows.