Adobe INDESIGN 2.0 - USING HELP Help Manual page 334

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Adjusting trapping tolerance
Some jobs need only the most extreme color changes trapped, while others require traps
for more subtle color changes. The Step Limit value specifies the threshold at which the
trapping engine decides to create a trap.
To change how much the component inks in abutting colors can vary before causing
those colors to trap, increase or decrease the value for Step Limit in the Trapping panel in
the Print dialog box. The lower the Step Limit percentage, the more often traps are
created between colors.
Using sliding traps
You can use a sliding trap to prevent abrupt shifts in trap placement along a gradient
edge. During trapping, the trapping engine adjusts (slides) the trap position—from
spreading the lighter color into the darker one, to straddling the centerline between them.
In the Trap Style dialog box, the Sliding Trap value 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%.
To set the percentage difference at which a trap slides:
1 Open the Trap Style dialog box for a new or existing style. (See
palette" on page 327.)
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.
Trapping imported graphics
You can create a trap style to control traps within images, and to control traps between
bitmap images, such as photographs, and vector objects, such as those from a drawing
program. If you're using built-in trapping instead of Adobe In-RIP Trapping, be sure to
understand the differences in the way each trapping engine handles imported graphics;
see "About trapping imported images" on page
The Trap Style dialog box includes the following options:
Trap Placement Provides options for determining where the trap falls when trapping
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.
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"Using the Trap Styles
324.
Trapping Color
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