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One of the most often asked questions I get is to explain the difference between the various printing and separation methods and the type of software used for each. Questions like, "is Corel Draw better than Adobe Photoshop" and "when should I use Simulated Process Color over Index Color separations"; are the norm. With so many articles about the different methods and so may automated software programs expounding the virtues of each method I thought it was time to try to clear the air about what they are.
Vector Based Programs
So which is the best program. There is no correct answer. When you read on you will see that different types of separations are done with different programs. Most computer graphic departments have both vector based programs for their text, cartoons, logos and hard edge graphics and pixel based programs for their photorealistic images. Don't forget, you can create part of the image in one program and take it into another to add additional elements.
Types of Separations
A spot color image can be as simple as one-color and as complex as ten colors, and can include lots of shading, gradations and detail. They still generally have a flat, cartoon like look and are not photorealistic.
Spot color separations are done in vector based programs like CorelDraw, Adobe Illustrator and Macromedia Freehand (figure 2).
If process color will print all these colors then why not use it for all your designs? If a T-shirt image were not photorealistic why would you want to print four colors when for a simple "spot color"; image only two would do? Also, for most of your spot colors images you need a more vibrant, solid image rather than a soft halftone dot print.
Process color prints on T-shirts generally only work well on light colored shirts. The inks used are very transparent and do not work on black, and when printed on an underbase of white ink, will become very pastel.
The problem with printing process is that if you are not a good printer or don't know how to do the separations, the images will be muddy when printed. Although process color separations are generally done by pixel based programs like Adobe Photoshop (figure 5), these programs were designed for paper/offset printing and the program settings don't allow for the fact that halftone dots grow in size when printed on a soft object like a T-shirt (dot gain). Process color separations are generally NOT done with vector based programs like Corel Draw.
For this reason, process color is not for everyone. It generally needs better control like properly tensioned, high mesh-count screens and the ability to hold fine halftone dots and print them in register with minimal dot gain. The secret to good process prints is in proper separations and good printing. Yes, you can do it, but plan to experiment a little.
When you see a hot process color print, it almost always has additional spot colors. What you think is just a cmyk print may in fact have cmyk plus two or three spot colors to make the design really jump off the shirt.
If you don't know how to do the separations you should either use an industry specific color separator, follow directions from articles in this magazine or download how-to-do-it articles from www.screenprinters.net/articles, or use industry specific separation software.
Simulated Process Color
Because the inks for simulated process color are generally all-purpose, semi-transparent plastisol they give you a bright print even when printed on an underbase of white ink. When done correctly, simulated process prints can be very photorealistic with smooth gradations and bright colors.
Index color separations are done in Adobe Photoshop by creating a color table of the most prominent colors in your image (and the most colors you are capable of printing) and then letting Photoshop convert the image to just those colors using random square dots. Photoshop will make (or try to make) the image look as close as the original as possible with just the limited number of colors you selected (figure 11).
Index prints can be very bright on light and dark shirts and the separations are easy to do. The downside to index prints is that for the image to be photorealistic you need at least six colors and in some cases eight to ten colors. Index prints can sometimes have a grainy and textured look to them. When printed with a lot of colors index prints can also be very striking (figure 12)! Index separations work great for spot color images too. They are also easy to print because you are placing a dot next to a dot rather than printing halftone dots on top of halftone dots. Just don't use indexing because someone told you that halftones are hard. Most of the award winning prints you see are still real process color and simulated process color.
When To Use What?
CMYK Process Color
Simulated Process Color