With the rapid growth of photo-inkjet printers using sixcolorant in response to the spread of digital and mobile cameras, there has been a lot of research regarding six-color separation in order to achieve visually smooth tones in highlight regions. Most conventional method use the maximum amount of colorant with a low dot-visibility, thus resulting in paper wetness, poor edge-sharpness, and ink spreading and blotting in printed images. In order to reduce the amount of unnecessary colorants, this paper proposes a photo-inkjet printing method based on the limited total amount and dot-visibility ordering of a six-colorant. First, CIELAB values are estimated for an input CMY image using a color-mixing model, then these values are compared with the precalculated CIELAB values that correspond to all combinations of the CMYKlclm (Cyan, Magenta, Yellow, blacK, light cyan, and light magenta) colorants. This is done by using a color-difference constraint, which can determine the initial CMYKlclm candidates. Next, limitations on the total amount of colorant are imposed on the initial CMYKlclm candidates in order to remove excessive colorant, then the final CMYKlclm candidates are determined by minimizing the usage of light cyan and light magenta in the dark regions, based on a dot-visibility ordering of C, M, Y, K, lc, and lm. Finally, a lookup table is generated. It is composed of the CMY values versus the CMYlclm digital values. Experiments showed that the proposed method could effectively reduce the use of unnecessary colorants, while preserving good image quality.
Joong-Hyun Kim, Chang-Hwan Son, Tae-Yong Park, Yeong-Ho Ha, "Photo-inkjet Printing Method Based on the Limited Total Amount and Dot-visibility of Six-colorant" in Proc. IS&T 15th Color and Imaging Conf., 2007, pp 255 - 260, https://doi.org/10.2352/CIC.2007.15.1.art00048