The expression of relative distortion based on even-power series of a radial radius is commonly used in camera calibration.

There is a level of non-linear distortion that is "good enough" relative to other flaws in the loudspeaker. Further reduction of this distortion brings no audible improvement.

This paper proposes an algorithm of iris automated identification and a method for rectification of geometric distortion of iris image. The matching result is measured by the relative coefficient.