Graphics Programs Reference
In-Depth Information
If we understand that a profile describes the behavior of a device, we
should be aware that if the device changes its behavior, the profile is no
longer valid. Calibration returns the device back to the original condi-
tion, maintaining the integrity of the profile. If the device can no longer
reach the original aim point, a new aim point within the capability of the
device needs to be created. With this new aim point, a new profile must
be created to reflect this new condition. It is important to understand the
distinction between calibration and profiling. It is important to under-
stand that a profile is usable only as long as the device remains consis-
tent. Profiling a device that is inconsistent or constantly drifting is an
exercise in futility. When color management fails, the first step in trou-
bleshooting should be to examine the calibration to the device and its
relationship to the ICC profile.
Some devices, like a scanner, are more consistent than other devices,
like a display. Some devices need calibration only when major changes
to the device occur. For example, scanners are quite stable devices. Some
high-end scanners will self-calibrate to account for temperature changes
in the light source. If the bulb needs to be changed, usually you will need
to reprofile the device. As we will see when discussing color management
and displays, it will be necessary to calibrate and profile a display on a
regular basis. Some printers vary in their consistency, thus the need
for calibration. Not all devices can be or need to be calibrated. If a device
is very consistent in how it behaves day in and day out, then only
a profile is required for use in a color management system. Some
devices calibrate automatically and require no end user calibration
process. Many high-end ink-jet printers fall into this category. These
printers work quite effectively with a good output profile. If something
within the printing process changes, new ink, new paper, an update to
the print driver, a new profile may be necessary. An example of a device
that does change due to media is a Fuji Pictrography printer. This unit
has a built-in hardware calibrator. Each time you replace its media (a
donor and a paper), you must print out a target and run that target
through the built-in calibration instrument. This process examines the
new media and accounts for differences found, then adjusts the printer
by calibrating it back to a factory default calibration. Once an ICC profile
is produced that describes this factory default behavior, any time new
media is loaded and a calibration procedure is conducted, that profile
remains valid and useful.
Calibration and profiling work hand in hand. Devices that can't be
calibrated and have inconsistent behaviors are poor candidates for any
kind of color management and should be avoided like the plague. In
addition to media that can change from batch to batch, environmental
conditions can also wreak havoc on the consistency of a device. Depend-
ing on the device, humidity and ambient temperature can affect a device's
behavior significantly.
Search WWH ::




Custom Search