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Trapping

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[Part 2 of 6]

Overprinting Black. By default, all objects on an InDesign page knock out of all objects behind them - unless they're black. InDesign, by default, overprints black ink. Most of the time, this is a good thing. To turn off black overprinting, display the General panel of the Preferences dialog box and turn off the Overprint Black option.

Spot-Color Trapping. It's more important to trap abutting color fields in publications you 're printing using spot colors than it is in process color publications. When you 're working with process colors, you'll almost always see some ink between abutting objects, so you're less likely to see paper-colored gaps showing a poor trap.

The easiest way to demonstrate how spot-color trapping works is to show you some examples.As you work through these examples, you'll trap an ellipse into a rectangle by manipulating the color, width, and overprinting specifications of the path that surrounds the ellipse.First,draw the colored objects.

  1. Create a rectangle. Fill the rectangle with a spot color ("Color 1").Set the rectangle's stroke color to None.

  2. Draw an ellipse on top of the rectangle. Make sure that the ellipse is entirely inside the rectangle.Fil l the ellipse with a dif ferent color from that of the rectangle ("Color 2"). Set the stroke of the ellipse to None.

  3. Save the file.

The ellipse needs to be trapped, or you'll run the risk of having paper-colored lines appear up around the ellipse when you print the publication. You can either spread or choke the ellipse,or both.

To spread the ellipse, follow these steps (see Color Example 3)).

  1. Select the ellipse.

  2. F10 to display the Stroke palette.

  3. Choose Weight Changes Bounding Box from the Stroke palette menu, then enter a new line width in the Weight field.

The line width you enter in the Weight field should be equal to twice the trap amount - if you enter "2", you'll get a stroke of one point on either side of the path. If your commercial printer has asked for a trap of .5 points, enter "1" in the Weight field.

When you print, the ellipse is larger than the hole that's been knocked out of the background rectangle, which means that the outside of the ellipse slightly overprints the background rectangle. You've just created a spread.

After you're through looking at the objects, or printing, choose Revert from the File menu and revert to the version of the file you saved earlier. This way, you're ready for the next procedure.

To choke the ellipse, follow these steps (see Color Example 3).

  1. Select the ellipse.

  2. F10 to display the Stroke palette. Make sure that Weight Changes Bounding Box option on the Stroke palette menu is turned on, then enter a new stroke width in the Weight field.

  3. In the Stroke Inspector, choose Basic from the Stroke Type pop-up menu,set the line color to "Color 1" (the color of the background rectangle), type a line width for your trap in the Weight field. Finally, turn on the Overprint option in the Attributes palette.

When you print, the hole that's knocked out of the background rectangle is slightly smaller than the ellipse. This way, the outside of the ellipse slightly overprints the background rectangle. You've just created a choke.

Choose Revert from the File menu to get the file ready for the next procedure.

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