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FLEXO Magazine : August 2008
TECHNOLOGIES & TECHNIQUES match the color of their press inks. They then spend time testing new donors, or fi nding a press ink set to match the proofer’s pri- maries. Or they do both. Then they rework their dot-gain curves. Months pass. This is the traditional color management workfl ow. Even after all this, most folks find that the proofs still aren’t a really tight match, particularly in saturated reds, greens, and blues (and often grays). This is generally due to wet versus dry trap issues. Today’s digital dot proof is basically a dry-trap process. When a customer’s file calls out for red (100 percent magenta, 100 percent yellow) or blue (100 percent cyan, 100 percent magenta), modern dot proofing systems transfer those exact values (100 percent of them) into the proof. But when one is printing on a non-UV press, wet ink is being laid down over another wet ink, and some percentage of the second ink doesn’t actually transfer to the pa- per. You may have plates that call out 200 percent coverage, but that isn’t what ends up adhered to the paper. For example, it is pretty standard to see 30 percent ink-holdback in blues (and com- pared to 200 percent coverage, 170 percent is a different color!) At this point most people begin to truly understand that two- dimensional dot-gain curves can only do so much, and tend to cause as many problems as they fix. So people wisely try to color manage their dot proofers with much more sophisticated three- dimensional ICC profiles. Which brings us to our first ICC-based color problem. With 3D profiles, the color match to press is fantastic (espe- cially reds, green, and blues) But upon closer examination, one begins to see that any incoming file which contains vignettes of pure primary colors (like cyan, yellow, or magenta) ends up with scum dots of contaminating color in those vignettes. Customers hate seeing a 2 percent cyan dot inside what should have been pure yellow. Next, one might notice that all objects, text, and drop-shadows that had originally been made of only black ink (in the incom- ing file), have now suddenly turned to four-color black/gray. Colorimetrically, the colors may look right, but customers and pressmen won’t accept that kind of proof. Upon seeing these results, most people immediately stop color managing their dot proofs and return to curves. But there is another solu- tion, which we’ll get to in a moment. First let’s explore another potential problem. PROBLEM TWO: TRICKY Many fl exographers are provided separations by the customer. Many times these separations are ter- rible. Perhaps because the customer edited them on a system that didn’t have a calibrated monitor, or maybe they were color corrected to match some random copier output from the customer’s of- fice. In either case, you’re doomed. Other times the cus- tomer-provided separa- tions are actually fine. The separations are properly done, properly color-cor- rected, and have attached profiles giving all down- stream printing vendors the information they need to know how the fi le was separated. The issue with
Flexo Sustainable Fall 2008