Fast Fourier demodulation

We present a fast Fourier demodulation method for calculating the distortion in a repetitive pattern. The technique is based on applying digital demodulation, then using only the anti-Hermitian part of the pattern in Fourier space. After demodulation, we are left with the Fourier transform of the sought phase information only. Using also the Hermitian part, we would have gotten the object itself. We investigate the boundaries of the technique, as related to aberration content, amplitude variations, and sensitivity to noise.