Removal of carrier frequency in phase-shifting techniques

The existence of carrier frequency is unavoidable in many phase-shifting techniques. It makes the phase-unwrapping procedure more difficult, especially when speckle-like noise exists in the wrapped phase map. In this paper, it is shown that the carrier frequency is approximately equal to the average of the first difference of the phase. To remove the carrier frequency, we compute the first difference of the phase before attaining the phase map, subtract the average of the first difference, and integrate to get the phase map without carrier frequency. Computer simulation and experimental results show this method as being profitable for phase unwrapping. (C) 1998 Elsevier Science Ltd. All rights reserved.