Set sliding traps, About trapping black, Set the trap width for colors next to black – Adobe InDesign CS3 User Manual
Page 476
INDESIGN CS3
User Guide
469
Set sliding traps
1
Choose New Preset in the panel menu to create a preset, or double-click a preset to edit it.
2
In the Trap Thresholds section, for Sliding Trap, enter a percentage from 0 to 100, or use the default of 70%. At
0%, all traps default to centerline; at 100%, sliding traps are turned off, forcing one color to be spread fully into
another regardless of the neutral density relationship of the abutting colors.
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