As described above, in a case in which such m pieces of gradation values from the first Gradation value to an m-th gradation value with m being an integer of 3 or more are the characteristics-acquired gradation values, and such a k-th gradation value is larger than a (k+1)-th gradation value with k being an integer of 1 or more and (m?1) or less, 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 with 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 k-th gradation value and the (k+1)-th gradation value, the equation that represents the relationship between the spectral reflectances of the k-th gradation value and the spectral reflectances of the process target gradation value with the spectral reflectances of the k-th gradation value being taken as the first reference and with the spectral reflectances of the (k+1)-th gradation value being taken as the second reference is obtained as the second relational equation; and regarding the process target gradation value between the m-th gradation value and the minimum gradation value, the equation that represents the relationship between the spectral reflectances of the m-th gradation value and the spectral reflectances of the process target gradation value with the spectral reflectances of the m-th gradation value being taken as the first reference and the spectral reflectances of the minimum gradation value being taken as the second reference is obtained as the second relational equation.