Interferometery fringes contains signal inform of amplitude or phase. The amplitude contains large amount of noise i.e. very difficult to remove. So it is better to use phase value of detected signal. There are many techniques of phase detection like Fourier transform Fringe skeletonization Phase-stepping Temporal heterodyning Spatial heterodyning (carrier frequency) Phase locking Phase-shifting The phase stepping method provide continuous phase detection of live fringes.