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FLEXO Magazine : August 2008
TECHNOLOGIES & TECHNIQUES these fi les is: they were separated for a process other than fl exo (probably SWOP). Either the dot gain compensation is inappropri- ate, or they weren’t separated for the correct hue of inks, making the color and gray-balance inappropriate. They also might have been separated for an ink rotation which isn’t being run, etc. If these “good” (but improper) separations are in a known ICC color space (i.e. U.S. SWOP v2), sophisticated flexographers will often try to use their workfl ow software to import and immedi- ately convert the whole job out of the inappropriate CMYK color space directly into an appropriate custom in-house flexo ICC profi le. By doing so, pure colorants become contaminated with scum dots and black-only text and graphics become four-color. Additionally, 400 percent registration marks get screened to less than 400 percent, and 100 percent black overprints re-separate to yield a screened-back black overprint. And, again, while the over- all color looks good, no pressman would want to try to register the print job. The reason these shifts happen is technical, but it involves the way color is transformed inside the color matching module (CMM) when normal ICC Output Profiles are used. What fl exographers need is some way of making an ICC profi le that is a more direct CMYK color transform, which can correctly color manage normal color, preserve “special” colors (like pure cyan, or black), and also preserve certain color “formulas” (i.e., 400 percent registration black, which is more of a “thing” than a color.) THE SOLUTION The guys who came up with the ICC specifications all those years ago were pretty clever. Years ago they defined a potential solution: the ICC Device Link. ICC Device Links are basically two ICC Output Profiles con- nected (or concatenated) into one file. When making a Device Link, one chooses a rendering intent and sets other desired specialty link settings and then the LAB data located inside both profi les is used to connect them together. Once the profi les are concatenated, the LAB data is then removed from the link—thus, you are left with a direct CMYK to CMYK look up table (LUT). It is because one is left with this pre-constructed, ready-to-go, CMYK-to-CMYK table that some really interesting, tricky things can be done. For example, the issue of secondary color contamination in vignettes of pure primary colors can be solved. The linking program can simply go into those color ranges and edit the exist- ing entries in the LUT to remove 6 6 F LEXO contaminates. It can also automatically adjust for dot gain differ- ences between two devices, without the end-user having to make any manual calculations or adjustments. Registration black can also be re-set to 400 percent. A 100 percent black overprint can be preserved, and scum dots in paper white can be automatically removed. Basically, because ICC Device Links are made from ICC Output Profiles, they give you all the benefits of ICC Profiles, but can eliminate many of the problem issues fl exo has had with color management. Why haven’t you heard much about Device Links? Device Links have been around for years, but as early as five years ago, very few programs supported Device Links. Today, almost all high-end workflow products include Device Link sup- port. Many inkjet rips support Device Links as well. Thus, today, almost every commonly used workflow will let you color manage your dot-proofs with no problem. And almost all of them allow you to “normalize” or “re-color manage” pre- separated customer jobs into a more appropriate “in-house” color space upon import. Some of the workflow products have optional modules which will let you apply ICC Device Links at the filmsetting or plateset- ting stage! That means you can apply sophisticated ICC color management at the last moment, once you decide which press you are going to run the job on. While this workflow is amazingly powerful, it is still new. There are potential problems with ruined object trapping when some- one color manages so late in the process, but feedback I have been hearing from people testing the “late binding” workfl ow are initially positive. How do I know if my software supports Device Links? Most programs clearly delineate between an ICC Output Profile and an ICC Device Link workflow and it is pretty clear to know where to put the different type of profi les. Other programs don’t support links at all and won’t let you import or use a Device Link in any part of the program. In both these cases, Device Link support is pretty clear. Yet, if you have a software program that doesn’t mention Device Links anywhere in its dialogs or instructions, it may still support them! Here is the trick: some programs which actually support Device Links but lack obvious interfaces to use them will normally allow you to import or place a Device Link in the field where you would normally put an ICC Source Profile. Try it…you may get lucky. ? ABOUT THE AUTHOR: Eric Magnusson is the president of Left Dakota, a California-based corporation dedicated for the last 10 years to color management consulting. He got his start in the industry in 1988 at Quark Inc. and worked for Prepress Technologies, Lightsource, and Live Picture before founding Left Dakota. AUGUS T 20 0 8 www. f l e x o g r a p h y. o r g
Flexo Sustainable Fall 2008