Eight Ways to Deal with Trapping

Because registration issues have been around for as long as there have been color presses, numerous strategies have evolved to ensure good-quality color output. Here are the most common ones.

1. Use Trapping Software

These days you can choose from a collection of sophisticated software whose job is to study a PostScript print file, determine the areas where colors butt against one another, and apply trap to those areas. The program will then create a modified version of the PostScript print file, which you can in turn send to the imagesetters at your service bureau. The software that runs on PCs, called TrapWise, is marketed by Luminous Technology Corporation. This is not typical, run-of-the-mill software—it costs nearly $4,000. Some businesses can justify that type of investment, but it’s more likely you would seek out a service bureau that has purchased TrapWise and will apply it to your work for a usage fee.

2. Find a Smart Imagesetter

Well-equipped service bureaus may use a special imagesetter made by Scitex. This machine reads composite print files (that is, ones that are not separated), separates the colors, and applies traps where needed. Then it sends output directly to a raster image processor that creates the film. Using the Scitex machine costs close to twice the usual $12 to $18 for a piece of film produced on a standard imagesetter.

3. Choose Common Colors

If your drawing’s color scheme has any flexibility, you can avoid trapping errors by choosing your colors with that in mind. When two objects share at least 20% of the same color, you have effectively eliminated the risk of registration errors.

For instance, let’s say that the big A on our cube doesn’t have to be pure magenta, but instead could have a slightly red tint of 100% magenta and 25% yellow. Now think about how the yellow ink would be laid down in that area: it would be at 100% intensity around the face of the cube and at 25% in the space where the A is to go.

Now when the A is laid down, it still needs to be placed in the knockout area, but because that area already contains yellow ink, a registration error is not going to be too unsightly. Remember, a bad registration error is one that produces white streaks where there is no ink present at all. In this case, though, the entire face has yellow ink, including the knockout area for the A. As you can see in Figure 27.9, the knocked-out area of the face has a small amount of ink coverage—enough to keep a small registration error from being too objectionable.

FIGURE 27.9  This knockout area of the cube is effectively trapped by using a common color. The entire face of the cube has some amount of yellow, eliminating the possibility of the paper color showing through.

Incidentally, the top face of the cube and the red B need no trapping because they share a common color—the B has yellow and magenta, and the top face also contains magenta. The same is true for the right face and the C, which share cyan.

4. Overprint Small Objects

Applying trap to your drawings can be a daunting task, but there is one situation that is easy to handle. When you have small text or other objects on a colored background, the trapping strategy is simple.

Figure 27.10 shows a two-color drawing with black body copy placed on a colored background. The simplicity of this piece belies the trouble it will cause when it goes on the press, and Figure 27.11 shows why. By default, DRAW creates separations using knockouts, as described in the preceding section. Imagine the registration nightmares of printing this piece, what with all of those fine serifs and thin ascenders in the 9-point text. This job would be virtually impossible to register properly.

FIGURE 27.10  What could possibly go wrong with printing this simple two-color job?

This project offers an ideal opportunity to use overprinting of your black text. Overprinting is the opposite of knocking out. Instead of creating white holes on the other color plates, you tell DRAW to ignore the black text on all other plates and pretend that it isn’t there. Let’s back up one step. Earlier in this chapter, we established that some objects had to be knocked out of other objects. Otherwise the transparent inks overlap, creating an unwanted color. But that doesn’t apply to black, because it absorbs all light. When you mix black with another color, you get black. Therefore, you don’t need to knock out small black text; instead, you can ask for it to be overprinted.

FIGURE 27.11  How would you like to try to line up these two plates on the press?

You can ask for overprinting in DRAW in two different ways:

•  On an object-by-object basis, you can instruct that outlines or fills be overprinted by clicking mouse Button 2 on the object and choosing Overprint Fill.

•  Globally, you can turn on the Always Overprint Black option in the Separations page of the Print dialog. With this option set, any object that contains at least 95% black will be set to overprint.

Figure 27.12 shows the effect of asking for text to be overprinted. By eliminating the knockout, you have also eliminated any registration issues.

Purists argue that black overprinted on another ink color produces a different type of black—referred to by some as a “juicy black.” Technically, they’re right, but the point is not really worth arguing for any but the most demanding of print jobs. Certainly, if you ask for a 72-point headline to be overprinted, you’re laying down a whole lot of black ink on top of other ink colors and that would be noticeable. This is why the Always Overprint Black option should be used carefully, and overprinting should only be used for small objects. Nevertheless, when you are working with smaller text, fine hairlines, rules around boxes, and other small black objects that are to be placed on top of other colors, overprinting is the answer to your trapping needs.

FIGURE 27.12  Bye-bye registration errors. With overprinted text (on the left), there are no fine serifs and other small objects to align.

5. Let Your Print Shop Take Care of Trapping

The next option in the trapping gambit is to do what designers and publishers have been doing for as long as there have been color presses: send your film to your print shop and ask them to trap your colors for you. The operators there will place your film under a powerful camera, study the areas where there might be problems due to misregistration, and apply tiny amounts of a common color to those areas. If your print shop employs skilled camera operators, this option is the friendliest of all, though not necessarily the cheapest. You’ll be charged from $30 to $150 or more per page for this service, but it’s usually the most reliable trapping option—and it’s not so terribly expensive when you factor in the hassles of doing it yourself and the cost of your time.