Decoding algorithm for interference patterns in phase shifting interferometry without a priori shift knowledge

Interferogram´s decoding methods based on the step-by-step shift are widely used in creation of interference measuring systems. The phase-shifting method is based on obtaining several interferograms when the phase of reference wave is changed to known values. Accuracy of existing decoding algorithms depends on a setting of values of inserted phase shifts. However, it is difficult to determine an exact value of the phase shift in practice because of errors of devices performing a phase shift. In this paper an algorithm based on the step phase-shifting without a priori knowledge of phase shift is considered. This algorithm uses three interferograms obtained with arbitrary phase shifts.