The same image on the display and color printer isn't the same. Firstly, this is due to the bit depth difference for
representing the color of a pixel. The display uses the color data of the eight or more bits, but the color printer uses just
1bit for representing color of a pixel. So, the display can reproduce smoother image than the color printer. Secondly, the
display gamut is larger than the printer gamut, so the display color is brighter and more saturate than the printer color.
For minimizing the problems due to these differences, many halftoning and gamut mapping techniques have been
developed. For the gamut mapping, color management standard organization, ICC, recommended 2 gamut mapping
methods, HPMINDE and SGCK. But the recommended methods by ICC have some weak points; contouring
(HPMINDE), paled pure color reproduction (SGCK) and too reddish hair color reproduction (HPMINDE, SGCK). This
paper introduces a gamut mapping method that can reproduce smooth gradation, pure colors with high saturation and
natural hair color. The proposed method is developed for optimal reproduction of graphic image, and it also gives good
results for pictorial image.
This study has three primary aims circumventing current limitations of color reproduction technologies: firstly, to derive base-line image quality factors from both color printer experts and academic research works. Individual factors were verified by systematic experiments, secondly, to develop a perceptual gamut mapping algorithm covering the image quality and preference factors derived, thirdly, to apply the algorithm to printer driver as acting for a vendor specific perceptual intent. Algorithm of this study tried to optimization between control parameters of gamut mapping and color
shifting factors of preference, e.g. skin, sky and green grass. Profile builder using this algorithm outperforms, in industrial and academic aspects, existing commercial tool and CIE recommended algorithms.
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.