To perform a highly accurate color conversion without the need for increasing a data amount of a color conversion table.

First image data by a first color system are converted into data of a cylindrical coordinate system whose coordinate axes are lightness, saturation, and hue, and further converted into second image data of a second color system while a color conversion table of the cylindrical coordinate system is referenced. The second image data set to each grating point of the color conversion table are stored in the state where data accuracy is differentiated in at least one coordinate axis direction of lightness, saturation, and hue. Since grating points set with high data accuracy are separated from grating points set with no high data accuracy in the coordinate axial direction by establishing the color conversion table by the cylindrical coordinate system, high accuracy regions and ordinary regions are provided in one table. As a result, the first image data is converted into the second image data with high accuracy while suppressing an increase in the data amount of the color conversion table.

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