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FLEXO Magazine : December 2012
Technologies & Techniques Extended Color Gamut Primaries FqC extended gamut Project by Danny Rich IntroduCtIon Traditional flexography has been applied mainly to packaging printing. In this application, the printing process incorporates both standard four-color process color printing for images and special spot color printing for brand identities, logos and graphics. With the advent and wide spread use of digital color man- agement, it has become possible to extend process printing beyond the three subtractive primaries of cyan, magenta and yellow inks, supplemented with a black ink; to include ad- ditional process primaries. Some of the early attempts at this were found in commercial offset printing, where image fidelity was of major importance. This approach was initially known as high fidelity printing. Examples include the “Big Top” ink set from Hallmark1 and Hexachrome® from Pantone® 2. In both of these applications, the standard process color inks were supplemented with fluorescent inks, including a fluorescent magenta and orange. But fluorescent inks have several disadvantages. They are not very stable to exposure to light and ultraviolet radiation, they are more expensive than conventional inks and they are more difficult to control in the ink kitchen. So, this approach was not widely used in packaging. It did, however, see some application in personal care products, as increased fidelity was important in the reproduction of faces and hair. Reports given at the annual IS&T Color Imaging Confer- ence3 documented the potential increase in color gamut achieved when using a fifth, sixth and seventh process color primary. Running simulations using a simple Neugebauer additive mixing model, comparisons between the various combinations of primaries were reported. The largest gamuts were obtained by adding an orange, a green and a violet primary to the cyan, magenta and yellow primaries. The second largest gamut was obtained using a neutral red, one that was neither yellowish nor bluish, a true green and a red shade blue primary. However, the studies focused mainly on publication and commercial printing. Some approaches, such as that by MY Cartons4 in Europe attempted to utilize a hybrid, where standard halftone images were printed by conventional four-color process inks using analog plates and the spot color graphics were printed using three additional primaries that were printed using frequency modulation (FM) screening. FQC’s sTEPs & RECs • Study examines theory for process printing and with 4+ inks and practical aspects of achieving greatest gamut increase • Field trial performed • Data gathered from 50+ printruns • Orange, green and violet inks deemed top performers • Recommendation = Seven ink set has acceptable reproduction accuracy and stability Figure 1: CielAB diagram showing position of the C,M,Y,K primaries and several extended gamut primaries R,o,g ,B ,V 12 FLeXO DeCeMBeR 2012 www.flexography.org