Adobe InDesign CS5 - Manual (Page 503)

497 USING INDESIGN
Trapping color
Last updated 11/16/2011
is darker than either color. Specifying a Trap Color Reduction lower than 100% begins to lighten the color of the trap;
a Trap Color Reduction value of 0% makes a trap with a neutral density equal to the neutral density of the darker color.
Trapping imported graphics
You can create a trap preset to control traps within images, and to control traps between bitmap images (such as
photographs and those saved in raster PDF files) and vector objects (such as those from a drawing program and vector
PDF files). Each trapping engine handles imported graphics differently. It’s important to be aware of these differences
when setting trapping options.
Trap Placement Provides options for determining where the trap falls when you trap vector objects (including objects
drawn in InDesign) to bitmap images. All options except Neutral Density create a visually consistent edge. Center
creates a trap that straddles the edge between objects and images. Choke causes objects to overlap the abutting image.
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.