Use Trapping in InDesign CS5

InDesign Creative Suite 5 has built-in software for trapping to improve the appearance of your printed documents. You can access trapping settings with the Trap Presets panel.

When you print documents, the printer is seldom absolutely perfect when creating a printed page with multiple inks. The registration (which determines the alignment of the separate colors when printed) will most surely be off. This discrepancy can potentially cause a gap between two colors on a page so that unprinted paper shows through between them.

To solve this problem, use trapping, which overlaps elements on the page slightly so that the gap doesn’t appear between elements. The basic principle of trapping is to spread the lighter of the colors into the other.

Text as it appears in InDesign (left). Text (right) as it appears when printed with trapping applie
Text as it appears in InDesign (left). Text (right) as it appears when printed with trapping applied.

The trapping settings you specify are applied to the entire page. You choose settings in the Trap Presets panel. You can use the default settings, customize the trapping settings, or decide not to use trapping.

To modify the default settings and then apply the customized settings, follow these steps:

  1. Choose Window→Output→Trap Presets.

    The Trap Presets panel opens. The trapping presets in InDesign are document-wide, but you can assign individual trappings by using the Attributes panel (choose Window→Attributes) to overprint strokes on selected art only.

  2. Double-click [Default] in the panel’s list.

    The Modify Trap Preset Options dialog box opens. The default settings are perfectly adequate for many printing jobs.

    The Modify Trap Preset Options dialog box.
    The Modify Trap Preset Options dialog box.
  3. Change the trap preset options, if you know what’s necessary, and then click OK to close the dialog box.

    If you don’t know what to change, investigate the options for a better understanding of how they work. You can also request settings from your print provider.

  4. In the Trap Presets panel, choose New Preset from the panel menu.

    The New Trap Preset dialog box opens.

  5. Type an appropriate name for the new trap preset.

    You see this name in the list of trap presets in the Trap Presets panel when it’s opened. You might create a name for a printer that has different settings from another.

  6. Review and make any changes to the new preset in the dialog box.

    You can change the presets by using these options:

    • Trap Width: The default value specifies the width of the trap for any ink, except black, that you use in the document. Enter the value for black in the Black text field.

    • Images: Control how InDesign handles trapping between elements on the document page and any imported graphics on it. Use the Trap Placement drop-down list to define how images trap to objects on the page. When bitmap images are next to each other, select the Trap Images to Images check box.

    • Trap Appearance: Do some fine-tuning and change how the corner points appear in trapping. Select the way corner points appear by using the Join Style drop-down list; select how end points appear (overlapped or separated) by using the End Style drop-down list.

    • Trap Thresholds: Control how InDesign traps the areas between two colors in a document. You can control whether InDesign traps two objects of similar colors (for example, how different the colors have to be before InDesign starts trapping).

  7. Click OK to create the trap preset.

    The New Trap Preset dialog box closes and the customized preset is added to the panel.

To assign a trap preset to a number of pages (or all of them), click the arrow in the upper right corner of the Trap Preset panel and choose Assign Trap Preset from the panel menu. in the dialog box that opens, choose a trapping style and assign it to all pages or a range of pages. Click the Assign button to assign the preset before clicking the Done button.

You have other ways to apply trapping to a document manually. This process goes beyond the scope of this book but is worthwhile to look into if you want to fully realize what trapping is all about.

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