About automatic trapping, Automatic trapping requirements – Adobe InDesign CS3 User Manual
Page 468
INDESIGN CS3
User Guide
461
Avoid the need for trapping by eliminating the possibility of misregistration in your use of color. Prevent misregis-
tration by making sure that abutting process colors have common inks. For example, if you specify a dark purple
stroke with a vivid red fill, they will both contain a significant percentage of magenta. The stroke’s and fill’s common
magenta will print as a single area, so that if misregistration occurs in the other process inks, the magenta printing
plate will make any resulting gap hard to see.
See also
“About overprinting” on page 577
About automatic trapping
InDesign can trap color documents with its built-in trapping engine, and can also take advantage of the Adobe
In-RIP Trapping engine available on Adobe PostScript output devices that support Adobe In-RIP Trapping.
Both trapping engines calculate adjustments to the edges of both type and graphics. They apply 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 requirements of specific
page ranges. You only see the effects of trapping on color separations generated by a trapping engine; you cannot see
the results on-screen within InDesign.
The trapping engine detects 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 panel modify the trapping engine’s results.
Automatic trapping requirements
To trap documents using the InDesign built-in engine, you need a PPD that supports separations.
To trap documents using the Adobe In-RIP Trapping engine, you need the following software and hardware:
•
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.
•
A PPD (PostScript Printer Description) file for a printer that supports Adobe In-RIP Trapping. You must select
this PPD when you install the printer.
See also
Differences between built-in trapping and Adobe In-RIP Trapping
Composite color workflow
With built-in trapping, you can separate a document by using InDesign or in-RIP
separations. To use Adobe In-RIP Trapping, you must use In-RIP separations.
Trap widths
Built-in trapping limits trap widths to 4 points, regardless of the value you enter for the trap widths. For
larger trap widths, use Adobe In-RIP Trapping.
Vector EPS graphics
Built-in trapping cannot trap placed vector EPS graphics; Adobe In-RIP Trapping traps all
imported graphics.