Some Trapping Notes from Adobe InDesign Help

Automatic trapping

InDesign can automatically trap color documents with its built-in trapping engine, and can also take advantage of the similar but more powerful Adobe In-RIP Trapping engine available on Adobe PostScript output devices that support Adobe In-RIP Trapping.

Both trapping engines can precisely calculate and apply any necessary adjustments to the edges of both type and graphics throughout your document. They can apply effective trapping techniques to different parts of a single object, even if text or an InDesign object overlaps several different background colors. Trapping adjustments are made automatically, and you can define trap presets to address the trapping requirements of specific page ranges. The effects of trapping are apparent only on color separations generated by a trapping engine; you cannot see the results on-screen within InDesign.

The trapping engine decides where to trap by detecting contrasting color edges, and then creates traps based on the neutral densities (lightness or darkness) of abutting colors, in most cases by spreading lighter colors into adjacent darker colors. The trapping settings you specify in the Trap Presets palette modify the trapping engine's results.

Trapping solutions

You can trap a document using any combination of methods, including the following:

§    Use process colors that don't need trapping. (See Using process colors that don't need trapping.)

§    Overprint black. (See Overprinting black.)

§    Manually overprint strokes or fills. (See Manually overprinting strokes or fills.)

§    Use InDesign built-in trapping or Adobe In-RIP Trapping.

§    Trap imported graphics, using the trapping features in the illustration programs in which they were created. Refer to the documentation for these applications.

Keep in mind that the trapping solution you choose must work well with the color output workflow you're using, such as PostScript or PDF. (See Two common print workflows.)

 

Requirements for trapping

To trap documents using the Adobe In-RIP Trapping engine, you need the following software and hardware:

§    A PPD (PostScript Printer Description) file for a printer that supports Adobe In-RIP Trapping. You must select this PPD by using the operating system driver. (See Selecting a PPD file.)

§    An Adobe PostScript Level 2 or later output device that uses a RIP that supports Adobe In-RIP Trapping. To find out if a PostScript output device supports Adobe In-RIP Trapping, contact the manufacturer or your prepress service provider.

§    To trap documents using the InDesign built-in engine, all you need is a PPD that supports separations.

(From Adobe InDesign CS Help. See your desktop publishing help file for more on trapping.)