About trapping black, Set the trap width for colors next to black, Printing books with conflicting trap presets – Adobe InDesign CS4 User Manual
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USING INDESIGN CS4
Trapping color
About trapping black
When creating or editing presets, the value you type for Black Color determines what is considered solid black and rich
black. A rich black is any black color that uses a support screen—additional percentages of one or more process inks to
strengthen the black.
The Black Color setting is useful when you must compensate for extreme dot gain (as when using low-grade paper
stock). These situations cause black percentages lower than 100% to print as solid areas. By screening back blacks or
rich blacks (using tints of solid black) and decreasing the Black Color setting from its default of 100%, you can
compensate for dot gain and ensure that the trapping engine will apply the proper trap width and placement to black
objects.
When a color reaches the Black Color value, the Black trap width value is applied to all abutting colors, and keepaway
traps are applied to rich black areas using the Black trap width value.
If support screens extend all the way to the edge of a black area, any misregistration causes the edges of support screens
to become visible, creating an unwanted halo or distorting the edges of objects. The trapping engine uses a keepaway,
or a holdback, for rich blacks to keep support screens a specified distance away from edges of reversed-out or light
elements in the foreground, so that the light elements retain their sharpness. You control the distance of support
screens from the edges of black areas by specifying the Black trap width value.
Note: If the element you’re trapping is a thin element, such as a black keyline around graphics, the trapping engine
overrides the Black trap width setting and limits the trap to half the width of the thin element.
Set the trap width for colors next to black
1 Choose New Preset in the panel menu to create a preset, or double-click a preset to edit it.
2 In the Trap Width section, for Black, enter a distance (in points) for how far you want other colors to spread into
black, or for how far you want support screens choked back under black. Typically, the Black trap width is set to be
1.5 to 2 times the value of the Default trap width.
3 For Black Color and Black Density, set values.
Note: To use black trapping features, a color area must use an ink with a neutral density greater than or equal to the Black
Density, and the ink must occur in percentages greater than or equal to the Black Color.
See also
Printing books with conflicting trap presets
You can apply one trap preset to one sheet of output, such as one page. Normally this is not a concern. However, if you
print multiple documents in a book, and each document or page has a different trap preset, InDesign can resolve some
trap preset conflicts by synchronizing presets among documents:
•
If documents in a book use different trap presets with the same name, InDesign assigns the trap preset used in the
master document, provided you’ve selected the Trap Preset option in the Synchronize Options dialog box.
•
The synchronizing feature makes all the master document’s presets available to the other documents in the book,
but does not assign them; you have to assign trap presets in each document, or use the [Default] trap preset. The
presets appear in the Trap Preset menu of the document’s Assign Trap Presets dialog box.
Note: If different trap presets are applied to pages in a spread, InDesign honors each trap preset.
Updated 18 June 2009