Black Extraction Method Using Gamut Boundary Descriptors

摘要

Color data conversion between CMYK and CIEL~*a~*b~* color space is not directly corresponded, that is many CMYK combinations could reproduce the same CIEL~*a~*b~* value. When building a LUT converting from CIEL~*a~*b~* to CMYK for a CMYK color printer, one to one correspondence between CMYK and CIEL~*a~*b~* must be aimed. The proposed method in this paper follows steps: (1) print and measure CIEL~*a~*b~* values of CMYK reference chart, (2) set-up parameters to assign the amount of black extraction, (3) generate gamut boundary descriptors for gamut mapping and for black extraction using CMYK-CIEL~*a~*b~* data under predetermined black extraction parameters, (4) perform gamut mapping for given CIEL~*a~*b~* using the gamut boundary descriptor for gamut mapping, (5) determine K value of the gamut-mapped CIEL~*a~*b~* using the gamut boundary descriptors for black extraction. The suggested method determines K value for given CIEL~*a~*b~* using gamut boundary descriptors in CIEL~*a~*b color space. As a result, a color printer using this method can make out accurate black amount and reproduces more consistent CMYK images under different black extraction options.