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Colorimeters
- A hardware device to calibrate
monitors
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Summary:
Computer monitors need to be adjusted, or
calibrated, for white and black set points and
neutral color. Once adjusted a monitor profile can
be used to "tell" graphic software and printers
about how your monitor displays colors. A device
called a colorimeter is used to to precisely
measure screen colors during calibration.
Jack
DeAngelis, PhD
OSU
Ext. Entomologist (ret.)
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There
are three separate procedures that you should
perform to get the best possible results from
your computer monitor. These are: (1) adjusting
the black and white set points; (2) color
cast removal; and (3) monitor
profiling.
While
procedures 1 and 2 may be preformed "by eye"
they are much more accurately done with a device
called a colorimeter. Steps 1 & 2
are sometimes called pre-calibration.
Monitor profiles, step 3, however, can only
be constructed using a colorimeter and
appropriate profiling software.
Black
and White Set Points - Have you ever used
a monitor that appeared to be too dark, or too
light, to clearly see detail? This is usually a
problem with black or white set points or contrast
and brightness in old TV lingo. These
adjustments can often be done inexpensively by
eye (see Related Articles below).
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Color
Cast Removal - A color cast occurs when a
neutral grey subject appears to have a color,
usually green, red or blue. If your monitor is
displaying a color cast you'll never be able
accurately see true colors on screen until it is
removed. Slight color casts can only be removed
using a colorimeter but large color casts can
sometimes be partially removed by eye.
Monitor
Profiles - The final step is to create a
computer file that tells other programs, like
image editors such as PhotoShop, how your monitor
displays colors or shades of grey. These programs
can then use the information to electronically
adjust an image whenever they display one that has
an "embedded" profile.
This
final step is called profiling. Profiling
is critically important for photography and
graphic arts, but less important for the average
user. Printers can, and should, be profiled as
well. Profiles are generated by software from
light intensity data collected by colorimeters.
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All of these procedures
depend on being able to accurately measure small
differences in color and light intensity coming from a
monitor. Human eyes are not very good at this because
our preception of color and light intensity is
strongly influenced by many external factors. Light
meters are much better because the extraneous factors
can be filtered out. Light meters that can measure the
intensity of specific colors of light are
called colorimeters.
In use the colorimeter is
attached to the monitor screen by suction cups.
Software then guides you through the process of
pre-calibration, calibration and profiling. The whole
process is fairly simple and re-calibration needs to
be done only about once a month.
All colorimeters work
pretty much the same. I can personally recommend the Colorvision
Spyder for high-end applications and the Spyder
2 Express is a new, easy-to-use, lower
cost unit for home use. Colorimeters come with
software for adjusting and profiling your monitor and
once completed you'll be able to work in image editing
programs like PhotoShop with confidence.
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