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Index Color: The Fastest Proof-to-Print System?

(February 2008) posted on Wed Feb 06, 2008

Index separations are often avoided by those who fear being stuck with too many colors to print. This month, Trimingham debunks some myths about index color and explains how to use it as an effective tool in prepress.

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By Thomas Trimingham

The order of steps in this process is important, because you don’t want to start the construction of the final illustration with a design that has too many colors. It’s far easier to edit the image before you put it into a design or combine it with typography. The final steps to setting up the wolf for placement were to duplicate and flip the side of the lower hairline and create a quick mask of a duplicate for extraction from the background. I duplicated the layer and used the Levels command to make it solid black and white, copied it to a channel, and created a selection for a knockout.

I then placed the extracted wolf onto the black background with the permanent typography so I could begin my separations (Figure 3). Index prints are a whiz to separate when they are properly prepared. This one was successfully separated into color channels in less than ten minutes. It started out as ten colors in the color table, which is fairly typical for an illustrated index separation, but that was where the finesse came in. I looked at each color individually to see whether it could be created by a combination of other colors or from a dropout of the underbase. The design settled in at seven colors after such adjustments. I could then save the seven colors as separate layers or channels that could then be imported into CorelDRAW or Adobe Illustrator.


Importing the final file into vector software

In Illustrator, I recommend using a DCS2.0 file with the separations saved as spot channels. The colors in these channels will show in the swatch menu and can then be used in overlapping typography or added vector elements. For CorelDRAW you would import the design with the indexed files saved as layers that are then converted to monochrome bitmaps with no fill. The outline color is the separation color. This makes a small file that prints out both separations and color proofs from the same page. One thing that I have found is thata full color layer set below the other layers will greatly improve the display properties of the file on screen without affecting file separation or printing. This has something to do with the way the computer combines the dots in index prints (Figure 4).


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