Adobe INDESIGN 2.0 - USING HELP Help Manual page 322

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Trapping Color
Compensating for ink misregistration by trapping
When a commercially printed document uses more than one ink on the same page, each
ink must be printed in register (perfectly aligned) with any other inks that it abuts, so that
there is no gap where the different inks meet. However, it's impossible to ensure exact
registration for every object on every sheet of paper running through a printing press, so
misregistration of inks can occur. Misregistration causes an unintended gap between inks.
You can compensate for misregistration by slightly expanding one object so that it
overlaps an object of a different color—in a process known as trapping. By default, placing
one ink over another knocks out, or removes, any inks underneath to prevent unwanted
color mixing; but trapping requires that inks overprint, or print on top of each other, so that
at least a partial overlap is achieved.
Misregistration with no trap (left) and with trap (right)
Most traps employ spreading—expanding a light object into a dark object. Because the
darker of two adjacent colors defines the visible edge of the object or text, expanding the
lighter color slightly into the darker color maintains the visual edge.
Trapping solutions
You can trap a document using any combination of methods, including the following:
Use process colors that don't need trapping. (See
•
trapping" on page 417.)
Overprint black. (See
•
Manually overprint strokes or fills. (See
•
page 419.)
Use InDesign built-in trapping or Adobe In-RIP Trapping.
•
Trap imported graphics, using the trapping features in the illustration or image-editing
•
programs in which they were created. Refer to the documentation for these
applications.
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"Overprinting black" on page
"Manually overprinting strokes or fills" on
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Trapping Color
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418.)
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