Six Color Separation Using Additional Colorants and Quantitative Granularity Metric

c d i d t s p T l b c bstract. This paper proposes a method of six-color separation sing additional colorants and a quantitative granularity metric to educe the color difference and graininess. In conventional six-color eparation, the use of light magenta and light cyan is generally an ffective way of reducing the visibility of dots in bilevel printing deices, i.e., light magenta and light cyan are used in a bright region nstead of magenta and cyan. However, the hue values for light agenta and light cyan differ from those for magenta and cyan in IELAB space, making the colorimetric reproduction less accurate. herefore, to minimize this inaccuracy, the proposed method uses ellow and light magenta colorants as additional colorants. In a right region, magenta is replaced with light magenta and yellow, hile cyan is replaced with light cyan and light magenta. These ombinations reduce the hue difference, as they create colors with a imilar hue to magenta and cyan. In addition, a smooth image can imultaneously be obtained owing to the lower dot visibility of the dditional colorants. In a middle region, magenta is replaced with ight magenta and magenta, while cyan is replaced with light cyan nd cyan. Since the use of these two colorants with different conentrations makes a coarse dot pattern, this phenomenon is reected based on a quantitative granularity metric. Finally, in a dark egion, only the magenta and cyan colorants are used as usual. xperiments show that the proposed method can simultaneously roduce a colorimetric and smooth tone reproduction. © 2006 Soiety for Imaging Science and Technology. DOI: 10.2352/J.ImagingSci.Technol. 2006 50:1 25