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FLEXO Magazine : August 2009
TECHNOLOgIEs & TECHNIQuEs from Excel. The same press variation will not only change the tint, but the color variation as well. Now, black compared to CMY is the most extreme, but it does explain why tint builds will change from pressrun to pressrun—and within a pressrun. The brain is more sensitive to “blocks” of color than to images. Look at the side-by-side photos of fl owers and leaves, with very wide ∆E (Figure 1), and look at some corresponding spot colors (Figure 2). Why do the spots look so differently? Because the brain does not focus on each element of a photo, but the entire image. There are three determinants of accurate spot color: ink gamut, color management and print consistency. Ink gamut. As it turns out, about 90 percent of all Pantone spot colors can be reproduced within 3∆E of a good set of extended gamut inks. Of course, there is the remaining 10 percent, but we can start off with pretty good coverage of the Pantone color chart. Color management. This might be considered heresy, but ICC profi les are not very good for seven-color process colors. The ICC standard was developed where the number of color dimensions equaled the number of inks. That’s fi ne when you print up to four colors. It’s only N4 dimensions. But what happens when you dramatically increase the number of inks? You get an exponentially larger number of points. It becomes unmanageable, so the ICC throws away 80-90 percent of the data, interpolating points when necessary. Thus, while the process may be good for CMYK, it’s not very good for seven-color matching (N7 There is a solution. Consider a model where there are multiple ). four color profi les, where only the relevant points are stored. For example, one table is CMYK, another replaces cyan with orange, another replaces magenta with green, and a fi nal one replaces yellow with blue. With this model, you can get about 90 percent more usable sample points from a test target and resulting profi le data of comparable sizes (Figures 3 and 4). Print consistency. We want to make spot color matching better, but the best color match is not necessarily best for the press. In our model where you can achieve a ∆E, we can make the print result more stable by eliminating color variation on press. Remember that tints vary more signifi cantly than solids? What if we try to build a color with one solid? With about half of the spot colors we can force greater accuracy. How about two solids? How about changing the rules? figUre 4. An example of four color possible profi les in which one table is CMYK, another replaces cyan with orange, a third replaces magenta with green, and a fi nal one replaces yellow with blue. changing The rULes What do we really know about extended gamut? Well, it’s more economical, because if you use common col- ors on all jobs, not only do you save on makeready time but, much more important, you can gang jobs together because you are using common inks. Proofi ng is not perfect, but we’re getting there. And thus we fi nally arrive at the message of this article. Visu- ally, spot colors created by extended gamut are not as accurate, but images can be much better. And, that typically leads to one further result: The package looks better! (Figure 5) figUre 3. A CMYK color profi le. figUre 5. the package on the left simply looks better, regardless of ∆E variation from the target. www. f l e x o g r a p h y. o r g Augus t 20 0 9 F LEXO 25