Color-to-colorant transformation for a seven ink process

Adding RGB inks to the traditional set of CMYK inks increases the attainable color gamut. But the added complexity poses a challenge in generating suitable separations for rendering of color images. The approach taken in this study reduces the dimensionality of the problem by subdividing the 7 inks into smaller groupings. A series of 4 ink subsets from the 7 ink superset of CMYKRGB were individually characterized and a colorimetric transform from ink to color was obtained for each subset. In color space the 4 ink subsets represent adjacent and overlapping subgamuts of the 7 ink gamut. By utilizing these characterizations both individually and in combination with one another, an inktable which transforms color to ink was generated. In the darker tonal region, 4 inks/color permits access to regions of the full 7 ink gamut which are inaccessible to schemes employing 3 inks/color.