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Color bars are also referred to as color
control bars, color control strips, or proofing bars. Color
bars are rows of different colored patches printed in the trim area
of the press sheet. They are used by proofers and press operators
to control the trapping,
ink density,
dot gain, and print contrast of the proof or the printed sheet.
They usually consist of solid and tint blocks of cyan, magenta, yellow,
and black; two and three color solids and tints; and additional elements
and patterns such as resolution targets and dot gain scales.
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Solid process colors of
Black, Yellow, Cyan, and
Magenta. A color bar are used to measure ink densities.
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Solid
overprint colors include blue (C&M), green (C&Y),
and red (M&Y) |
Screen
tint patches usually 25%, 50%, and 75% of the process colors.
A color bar are used to check for dot gain. |
A
color patch made up of 50C/30M/30Y. A color cast in the patches
will show an imbalance in one of the colors, either from incorrect
ink density or from dot gain. |
There are several different types of color bars and
which one to use depends on the type of printing being used. Prepress
and print suppliers purchase original film or the rights to digital
files of color bars and other test images. The film and files can
then serve as constant reference points throughout the proofing,
platemaking,
and print processes.
They are available from GATF (Graphic Arts Technical Foundation),
DuPont, RIT (Rochester Institute of Technology), and others.
Color bars are an essential troubleshooting
tool. They are easy to analyze, both visually and with a densitometer,
which is an instrument used for measuring the relative density of
any part of an image.
Color bars created for computer-to-plate
(CTP) systems may require additional features than color bars generated
for film.
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