To efficiently prepare a color conversion table with thigh accuracy.

A printer prints out a color patch (in 93=729 colors) distribute uniformly in an RGB color space and the color of the print result is measured. A polygon, denoting a color reproduction area of the printer, is generated on the basis of the colorimetric value. Whether a point P (Lab value) exists in the color reproduction area is confirmed. A color (nearest point R), closest to the point P in the color patch in 729 colors, is searched. A cube including the nearest point R is specified, and the Lab value corresponding to the RGB value in the inside is obtained by an interpolation arithmetic operation. The nearest point R of the point P (Lab value) is searched from a Lab value group obtained by the interpolation arithmetic operation. A color conversion table stores the RGB value of the nearest point R (this is considered as a point Q).