Working with color
trapping and overprinting
When colors are
trapped, they are intentionally overlapped so that misalignments of print
separations are not noticeable. In manual trapping, one color must overprint the
other. Overprint trapping works best when the top color is much darker than the
underlying color; otherwise, an undesirable third color may result (for example,
cyan over yellow results in a green object). In some cases, you might actually
want to create a third color; for example, you can overprint two spot colors to
create a third color.
colors mix depends on the type of colors and ink you are mixing and the types of
objects you are overprinting. For example, an object that uses a CMYK color
overprints differently from an object that uses a spot color. Bitmaps also
overprint differently from vector objects. You can preview a simulation of how
overprinted colors will mix by using the Enhanced with overprints viewing
mode. For more information about choosing a viewing mode, see "Choosing viewing
modes." Some variation between the preview and the printed version may occur,
depending on the printer you use.
When you are ready to
print, you can choose to preserve overprint settings if you want to trap objects
in a document, or if you want to mix the overlapping colors for effect. You can
also choose to knock out the overprinted areas so that only the top color is
visible. If you want to print a proof version of the file, you can simulate
overprints. Simulating overprints rasterizes the file and it prints using
process colors only.
You can set a group
of objects to overprint. You can overprint bitmaps; or each vector object’s
fill, or outline, or both. You can also overprint specific color separations and
specify in which order they will print, as well as whether you want to overprint
graphics, or text, or both.
The two methods for
color trapping automatically are always overprinting black and auto-spreading.
Always overprinting black creates a color trap by causing any object that
contains 95% black or more to overprint any underlying objects. This option is
useful for artwork containing a lot of black text, but it should be used with
caution on artwork with a high graphics content. You can adjust the threshold,
if the service bureau recommends a black threshold value other than 95%.
creates color trapping by assigning an outline to an object that is the same
color as the object's fill and having it overprint underlying objects.
Auto-spreading is created for all objects in the file that meet three
conditions: they do not already have an outline, are filled with a uniform fill,
and have not already been designated to overprint.
For advanced trapping
options, see "Specifying In-RIP trapping settings.