Phase-shift error calibration in modulation measurement profilometry

Modulation value play a significant role in Modulation Measurement Profilometry. By projection sinusoidal fringe on an object, then shift the sinusoidal grating in one period L(L >= 3) times with equal interval, we can calculate the modulation distribution on the object with these L frames of the fringe pattern. Incorrect modulation can arise when phase-shift error exist. In this paper we give out the general expression of modulation calculation for any phase- shift interval with least-square method when L equals 5. The result proved that the calibration is necessary and useful when phase-shift error exist.