A novel method to demodulate undersampled interferograms using a compu
ter-stored undersampled compensator is presented. First, the sine and
cosine of the computer-stored wave front is correlated with the interf
erogram that emerges from the asphere under test. Afterward, these two
correlation images are used to find the phase map. The detected phase
of the correlation fringes is the estimated phase difference between
the software compensator and the frame-grabbed interferogram. The prio
r information required for this method is a good knowledge of the wave
front being tested to a few wavelengths of error. Complying with this
prior knowledge, the undersampled interferogram under analysis may be
easily demodulated. Given that the proposed method is based on the co
rrelation of the frame-grabbed interferogram and the computer-stored o
ne, the method also withstands noise