Self-calibrating algorithm for three-sample phase-shift interferometry by contrast levelling

A new statistical self-calibrating algorithm for phase-shift interferometry is presented. The algorithm can be applied to the case of three phase-shifted interferograms for which the assumption of a constant fringe contrast over the viewing field can be made. Self-calibration is achieved by minimizing the non-uniformity that appears in the map of the calculated contrast when incorrect phase shifts are supposed. No information on the actual phase shifts has to be supplied, the only input needed is the set of three interferograms. The residual errors of the algorithm are as low as 2 pi/1800 in usual conditions.