Method for setting color conversion condition for use in image forming device, and image forming device

An image forming apparatus, comprising:

• a first color conversion unit that converts input image data expressed in a RGB color space into first output image data expressed in a multicolor color space including C, M, Y, and K, by using a first three-dimensional LUT, a color conversion relationship X being defined between the input image data and first colorimetric data of an image formed on the basis of the first output image data;
• a second-first color conversion unit that converts the input image data into intermediate image data α expressed in a device-independent color space, by using a predetermined conversion method, with a color conversion relationship between the input image data and the intermediate image data α being set as a color conversion relationship S;
• a second-second color conversion unit that converts the intermediate image data α into intermediate image data β expressed in the RGB color space, by using a second three-dimensional LUT;
• a second-third color conversion unit that converts the intermediate image data β into second output image data expressed in the multicolor color space including C, M, Y, and K, by using a conversion processing for conversion from the RGB color space into the multicolor color space including C, M, Y, and K without using a multi-dimensional LUT, a color conversion relationship Y being defined between the intermediate image data β and second colorimetric data of an image that is formed on the basis of the second output image data that is obtained by converting the intermediate image data β the same as the input image data by the second-third color conversion unit;
• and
• an image forming unit that is configured to form an image based on the first output image data if the image forming unit receives the first output image data and to form an image based on the second output image data if the image forming unit receives the second output image data,
• the second three-dimensional LUT indicating a relationship between the intermediate image data α and the intermediate image data β, the relationship between the intermediate image data α and the intermediate image data β being dependent on the color conversion relationship S, the color conversion relationship X, and the color conversion relationship Y, thereby ensuring that first colorimetric data of an image formed on the basis of the first output image data obtained by converting the input image data by the first color conversion unit is equal to third colorimetric data of an image that is formed on the basis of the second output image data obtained by sequentially converting the same input image data by the second-first color conversion unit, the second-second color conversion unit, and the second-third color conversion unit, wherein the second three-dimensional LUT indicates the relationship between the intermediate image data α and the intermediate image data β, the relationship being represented by S−1·X·Y−1.

A non-transitory computer readable storage medium storing a set of program instructions executable on a data processing device and usable for setting a color conversion condition for use in an image forming device, the image forming device including:

• a first color conversion unit that converts input image data expressed in a RGB color space into first output image data expressed in a multicolor color space including C, M, Y, and K, by using a first three-dimensional LUT;
• a second-first color conversion unit that converts the input image data into intermediate image data α expressed in a device-independent color space, by using a predetermined conversion method, with a color conversion relationship between the input image data and the intermediate image data α being set as a color conversion relationship S;
• a second-second color conversion unit that converts the intermediate image data α into intermediate image data β expressed in the RGB color space, by using a second three-dimensional LUT;
• a second-third color conversion unit that converts the intermediate image data β into second output image data expressed in the multicolor color space including C, M, Y, and K, by using a conversion processing for conversion from the RGB color space into the multicolor color space including C, M, Y, and K without using a multi-dimensional LUT;
• and
• an image forming unit that is configured to form an image based on the first output image data if the image forming unit receives the first output image data and to form an image based on the second output image data if the image forming unit receives the second output image data,
• the instructions comprising:
• obtaining a color conversion relationship X between the input image data and first colorimetric data of an image that is formed on the basis of the first output image data that is obtained by converting the input image data by the first color conversion unit;
• obtaining a color conversion relationship Y between the intermediate image data β and second colorimetric data of an image that is formed on the basis of the second output image data that is obtained by converting the intermediate image data β the same as the input image data by the second-third color conversion unit;
• and
• setting, in a form of values expressing a color conversion relationship on the second three-dimensional LUT, a relationship between the intermediate image data α and the intermediate image data β, by using the color conversion relationship S, the color conversion relationship X, and the color conversion relationship Y, to ensure that first colorimetric data of an image formed on the basis of the first output image data obtained by converting the input image data by the first color conversion unit is equal to third colorimetric data of an image that is formed on the basis of the second output image data obtained by sequentially converting the same input image data by the second-first color conversion unit, the second-second color conversion unit, and the second-third color conversion unit, wherein the relationship between the intermediate image data α and the intermediate image data β in the second three-dimensional LUT is set to have conversion characteristics represented by S−1·X·Y−1.