Adobe InDesign CC 2015 - Manual (Page 608)

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Printing
Last updated 6/6/2015
Neutral Density applies the same trapping rules as used elsewhere in the document. Trapping an object to a photograph
with the Neutral Density setting can result in noticeably uneven edges as the trap moves from one side of the edge to
another. Spread causes the bitmap image to overlap the abutting object.
Trap Objects To Images Ensures that vector objects (such as frames used as keylines) trap to images, using the Trap
Placement settings. If vector objects don’t overlap images in a trapping page range, consider turning this option off to
speed trapping of that page range.
Trap Images To Images Turns on trapping along the boundary of overlapping or abutting bitmap images. This feature
is on by default.
Trap Images Internally Turns on trapping among colors within each individual bitmap image (not just where they
touch vector artwork and text). Use this option only for page ranges containing simple, high-contrast images, such as
screen shots or cartoons. Leave it unselected for continuous-tone and other complicated images, as it will create bad
traps. Trapping is faster when this option is unselected.
Trap 1-Bit Images Ensures that 1-bit images trap to abutting objects. This option doesn’t use the Image Trap Placement
settings, because 1-bit images use only one color. In most cases, leave this option selected. In some cases, such as with
1-bit images where pixels are widely spaced, selecting this option may darken the image and slow the trapping.
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.