Adobe InDesign - Manual (Page 749)

Black Color
Black Density
Sliding Trap
Trap Color Reduction
Trap Placement
Trap Objects To Images
Trap Images To Images
Trap Images Internally
Trap 1-Bit Images
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in the New Trap Preset or Modify Trap Preset Options dialog box. The default is 10%. For best results, use a value from 8% to 20%. Lower
percentages increase sensitivity to color differences and result in more traps.
Indicates the minimum amount of black ink required before the Black trap width setting is applied. The default value is 100%. For
best results, use a value no lower than 70%.
Indicates the neutral density value at or above which InDesign considers an ink to be black. For example, if you want a dark spot
ink to use the Black trap width setting, enter the neutral density value here. This value is typically set near the default of 1.6.
Determines when the trapping engine starts to straddle the centerline of the color boundary. The value refers to the proportion of the
lighter color’s neutral density value to a darker, abutting color’s neutral density value. For example, setting the Sliding Trap value to 70% moves
the point at which the trap begins to straddle the centerline to where the lighter color exceeds 70% of the darker color in neutral density (lighter
color’s neutral density divided by darker color’s neutral density > 0.70). Colors of identical neutral density will always have their traps exactly
straddle the centerline, unless the Sliding Trap is set to 100%.
Indicates the degree to which components from abutting colors are used to reduce the trap color. This setting is useful for
preventing certain abutting colors (such as pastels) from making an unsightly trap that 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.
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.
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.
Turns on trapping along the boundary of overlapping or abutting bitmap images. This feature is on by default.
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.
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.
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