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FLEXO Magazine : February 2014
unique substrates like non woven (or metalized, etc.), where the read- ings of the spectrophotometers and the color management via software are only approximate and cannot communicate the exact finished appearance that only the human eye can be the final judge of Since only RGB additive color synthe- sis has biunivocal color combinations, a complete subtractive color chart for five inks—like Pentachrome—would be al- most impossible to construct for printing on standard substrates like polyethylene, since a chart for five inks with just nine steps for each ink between zero per- cent and 100 percent would take 95, or 9x9x9x9x9, which equals 59,049 patches. With a non woven substrate fewer steps are required because of its rough surface and high dot gain, which makes subtle differences irrelevant. By using just five steps, choosing only analogous color combinations and avoiding mixing complementary inks, which would increase grayness in detriment of sat- uration, a Pentachrome color chart for non woven substrates can have a much more manageable number of patches: • Around 875 total • 125 CMY patches • The same number for warm reds, cold reds, bluish greens, blues and purples, warm browns, etc. built with CMY plus two custom spot inks The criteria for building the color chart can be adapted to the type of graphics used in different industries. Black ink, if present, is usually used only as a solid color for, example, outlines, and thus is not part of the Pentachrome color builds. IMPLEMENTING PENTACHROME— STEP 2 The second step involves scanning the printed color chart using an auto- matic spectrophotometer connected to a standard profiling software with multicolor capabilities. From this, a multicolor ICC Profile is made that represents the fingerprint of the press on the specific printing conditions to be used later to print the job. Among other things, this includes: • Anilox rollers • Press settings • Ink types • Viscosities The optimal parameters for building the profile depend on the software used, including the algorithms, color engine, black generation, Illuminant, Rendering Intent, etc. In our experience we have used a color engine with algorithms optimized for multicolor, UCR (under color remov- www.flexography.org FEBRUARY 2014 FLEXO 43 Image 6: A screenshot of the tool used to calculate a first approximation to the required color builds in order to increase vibrancy while keeping Delta E divergence as small as possible