Color conversion table creation method, printing method, and color conversion method

A color conversion method for converting input data including only color values of process colors into print data including color values of a spot color and color values of process colors, comprising:

• an evaluation step of evaluating granularity for each area representing a combination of a color value of a spot color and a color value of process colors,
• an unusable region setting step of determining an unusable region that is a part of a plurality of areas each representing a combination of a color value of a spot color and a color value of process colors, based on evaluation results obtained in the evaluation step,
• an association step of determining corresponding relationships among a color value of process colors before color conversion, a color value of a spot color after the color conversion, and a color value of process colors after the color conversion so that each combination of a color value of a spot color and a color value of process colors after the color conversion is not included in the unusable region,
• a table creation step of creating a color conversion table so that the corresponding relationships determined in the association step are satisfied,
• a color chart printing step of printing a color chart by a target printing device after applying the color conversion table created in the table creation step to data for creating the color chart,
• a colorimetry step of performing colorimetry of the color chart,
• a color profile creation step of creating a color profile for output, based on colorimetry results obtained in the colorimetry step,
• a first conversion step of converting the input data into device-independent data using a color profile for input,
• a second conversion step of converting the device-independent data into the first print data using the color profile for output created in the color profile creation step, and
• a third conversion step of converting, using the color conversion table created in the table creation step, the first print data into the second print data that is used to print by the target printing device.