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