Herein, we focus on one intermediate gradation value that is a characteristics-acquired gradation value from among nine intermediate gradation values. Hereinafter, this focused intermediate gradation value will be referred to as a “focused gradation value.” Regarding such a Graph as illustrated in the portion B in FIG. 5, it is assumed that the curves for the maximum gradation value and the focused gradation value are as illustrated in FIG. 6 in the vicinity of a wavelength of 480 nm. In this case, the reflectance of the maximum gradation value is 0.15 and the reflectance of the focused gradation value is 0.52. In the present embodiment, such data obtained by combining the reflectance of the maximum gradation value and the reflectance of the focused gradation value with each other is treated as “combination data.” As mentioned above, data of the spectral reflectances is composed of 36 reflectances. Therefore, 36 pieces of combination data of the reflectances (the reflectances after normalization) of the maximum gradation values and the reflectances (the reflectances after normalization) of the focused gradation values are obtained. As illustrated in FIG. 7, each of the combination data is represented as one plot on a graph in which a horizontal axis represents the reflectance of the maximum gradation value and a vertical axis represents the reflectance of the focused gradation value. Hereinafter, the graph will be referred to as a “relational graph” for convenience. For example, the combination data based on the data illustrated in FIG. 6 is represented, on the relational graph, as a plot denoted by reference numeral 53 in FIG. 8. In this manner, in the present embodiment, 36 plots are represented on the relational graph. The calculation of the first relational equation corresponds to obtaining a curve (for example, a curve denoted by reference numeral 54 in FIG. 7) that passes through positions as close to the positions of these 36 plots as possible.