User`s manual

124 ScanWizard Pro for Mac OS X
Controlling UCR & GCR
Controlling UCR and GCR with Professional CMYK Profiles
In the final stages of color prepress production, the issues change: And your role
changes with them. You become that of a professional separator. And it becomes a
question of how skilled you are at making good films, films that run correctly on
press, avoiding downtime, rework, and expense.
Kodak Digital Science Professional CMYK Profiles helps you with your
separations. It expands your selection of undercolor removal (UCR) and gray
component replacement (GCR) options, so you can produce correct, quality
separations.
Some Background
It is difficult to print four wet layers of ink on top of one another. This is one of
the physical constraints of the printing process.
In theory, if you printed a 100% of each CMYK layer, you would have 400%
Total Area Coverage (TAC). Real-world experience proves this to be impractical.
It is difficult to print jobs that have more than 340% TAC, and most printers feel
more comfortable with 280% TAC.
Another area of practical concern is in how process inks are combined. Most
printers can not produce a clear, dense black from cyan, magenta, and yellow.
Black is needed to produce better details, contrast, and to get a desirable density.
Adding black to CMY reduces ink coverage TAC, and thus improves the ability of
paper to firmly hold each layer of wet ink, known as ink trapping.
So, from the concerns about ink coverage and ink combinations have come
tried-and-true approaches to producing excellent films for excellent separations.
Two aspects of the offset printing process are undercolor removal (UCR) and gray
component replacement (GCR).
UCR
Undercolor removal is the practice of removing quantities of yellow, magenta, and
cyan ink from the dark neutral areas in a reproduction and replacing what was
removed with an appropriate amount of black. Kodak implements UCR in its
Color Profiles within a TAC constraint: CMY gets replaced by the maximum
amount of K up to the TAC limit—so you get the highest possible density.
The neutral center of both diagrams show different UCR/TAC settings. With UCR
applied, less process inks and more black increases the density in the shadows.