## Calibration
is not necessarily linearization

To *calibrate *a system or subsystem, you bring it into conformance,
within a certain tolerance, with a predefined characteristic.

Sometimes, we wish to calibrate a device whose intrinsic response
is linear - for example, your bathroom scale. This special case of
calibration is called *linearization.* Other times, we wish to calibrate
a device whose intrinsic response is nonlinear. The float that measures
the fuel level in your car's tank is intrinsically nonlinear, but ideally,
the fuel gauge would be linear. We would like to linearize the fuel gauge.

A piano is designed so that each key produces a fundamental frequency related by
a fixed ratio to the frequency of the fundamental frequency of key to its left.
The ratio is the twelfth-root-of-two, or about 1.06.
A piano tuner can be said to "calibrate" the piano: He
causes each key to produce the correct frequency. First, he tunes the frequency
of A above middle C to be 440 Hz. Then, he imposes the twelfth-root-of-two
relationship between adjacent semitones. The piano tuner *calibrates* the
piano, but does not *linearize* it!

The Barco "Calibrator" is a high-end monitor with excellent
calibration facilities. When calibrated, is's not linear - it's calibrated
to a conventional CRT 2.5-power function. It's *calibrated,* but
not *linearized.*

*Timo considers "calibration"
and "linear" to be synonymous.*

*See also: Gamma FAQ
- Linear and nonlinear coding*

Charles Poynton

Copyright © 1998-07-27