To improve color reproduction, many printers today use extra colorants, in addition to the traditional four inks (Cyan, Magenta, Yellow and Black). Adding the complementary colorants (Red, Green and Blue) increases the gamut of reproducible colors, while lighter versions of the primary inks can be added to reduce graininess and dot visibility. Using more than three inks introduces colorimetric redundancy in the color separation process, because different ink combinations can reproduce the same target color. When additional inks are introduced, this redundancy rapidly increases, and it is thus crucial to introduce additional constraints in the color separation process, to improve determinacy and to optimize different aspects of print quality. This study focuses on an analysis of the redundancy in the color separation process for an 11-ink printer. It is investigated how the extensive colorimetric redundancy can be utilized to select optimal ink combinations to meet the, sometimes contradictory, criteria of color accuracy, graininess and ink consumption. Analysis of the results of applying different criteria in the color separation process shows that the result heavily depends on the selected criterion. For example, prioritizing graininess will improve print quality by reducing dot visibility, imposing the use of lighter inks, but it will also increase ink consumption.
Daniel Nyström, Paula Zitinski Elias, Sasan Gooran, "Addressing the colorimetric redundancy in 11-ink color separation" in Proc. IS&T Int’l. Symp. on Electronic Imaging: Color Imaging XXII: Displaying, Processing, Hardcopy, and Applications, 2017, pp 184 - 189, https://doi.org/10.2352/ISSN.2470-1173.2017.18.COLOR-058