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About
Trapping for Print
In
commercial printing, the process of adding a slight overlap between
adjacent areas of color to avoid gaps caused by registration errors
is called trapping. Color trapping is necessary to compensate for
poor color registration. Poor color registration occurs when the
printing plates used to print each color are not aligned perfectly.
Poor registration causes unintentional white slivers to appear between
adjoining colors.
Trapping is accomplished by intentionally overlapping
colors so that minor problems with alignment are not noticed. Many
service bureaus prefer to create color trapping themselves by using
a specialized trapping program. Most trapping today is done by software
for automatic trapping or PDF trapping. Trapping for print is a critical
part of the printing process!
With I-Trap™ you can trap your jobs in the print shop yourself!
Find out more about how customers use this powerful application here
Traditional Trapping
Traditionally
trapping was done as an optical process by providing a slight distance
between the image emulsion in the film and the actual plate material.
In the US this was an intentional process due to use of negative
film which places the emulsion layer of the film in direct contact
with the plate material. This required the intentional insertion
of an additional clear film between the negatives and the plate.
This rasied the negative emulsion slightly away from the plate.
During the exposure process this rasied negative allowed the exposing
light to slightly shine under the edge of the emulsion. This "fattening"
resulted in the traps.
In Europe and
other countries it is normal that the plate making process was done
with positive film rather than negative film. Using positive film
results in the emulsion side not being in direct contact with the
plate material and so the actual positive film does it own "fattening"
during the exposure process.
It was often
said in the past that "Trapping is an American Problem"
which is far from the case. Now that most of the world is moving
to CTP and film based plating is disappearing, nearly everyone needs
trapping!
Over Print Trapping
Over print trapping
in applications is achieved by different methods. Normally, portions
of an object that are obscured by another object are not printed.
However, if the top object is set to overprint, the obscured portions
of any underlying objects print anyway, causing an overlap. This
makes white gaps between different colors impossible. Overprinting
works best when the top color is much darker than the underlying
color, otherwise an undesirable third color might result (e.g.,
red over yellow might result in an orange object).
Depending on
the color-trapping options you choose, overprinting can affect an
object’s outline or its fill. This means that if an object with
a red outline is set to overprint its outline only, then any portions
of another object that are obscured by the first object’s outline
are printed. This overlap creates a color trap.
A few of the
types of trapping and over printing are at this link.
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