Calibration
vs. Characterization
Some of the terminology can be confusing. Many people are initially
confused about the difference between Calibration
and Characterization.
What is Calibration ?
Calibration is the process of modifying the color behavior of a device.
This is typically done using two mechanisms:
1) Changing controls or internal settings that it
has.
2) Applying curves to its color channels.
The idea of calibration is to put a device is a defined state with
regard to its color response. Often this is used as a day to day means
of retaining reproducible behavior. Typically calibration will be
stored in device or systems specific file formats that record the
device settings and/or per channel calibration curves.
What is Characterization ?
Characterization (or profiling) is recording the way a device
reproduces or responds to color. Typically the result is stored in a
device ICC profile. Such a
profile does not in itself modify color in any way. What it does is
allow a system such as a CMM (Color Management Module) or color aware
application
to modify color when combined with another device profile. Only by
knowing the characteristics of two devices, can a way of transferring
color from one device representation to another be achieved.
Note that a characterization (profile) will only be valid for a device
if it is in the same state of calibration as it was when it was
characterized.
What about display calibration and profiles ?
In the case of display profiles there is some additional confusion
because often the calibration
information is stored in the profile
for convenience. By convention it is stored in a tag called the 'vcgt'
tag. Although it is stored in the profile, none of the normal ICC based tools or applications are
aware of it, or do anything with it, it is just "along for the ride".
Similarly, typical display calibration tools and applications will not
be aware of, or do anything with the ICC characterization (profile)
information.