A new phase unwrapping algorithm based on Three Wavelength Phase Shift Profilometry method
Phase Shift Profilometry (PSP) method is widely used in 3D shape measurement. The advantage of the PSP method is that it is less sensitive to the surface reflectivity variations and the object can be measured point by point. But if only a single wavelength λ1 is used, the step height cannot be larger than λ1/4. In order to measure step height object, Gray Code (GC) and Multi-Wavelength Phase Shift Profilometry (MWPSP) method are used. But the GC method cannot solve the problem of the objects with a variety of colors under different illumination. The shortcoming of MWPSP method is that its speed is too slow because a lot of images with multi-wavelengths should be captured by the system. In order to solve the problem of measurement speed and measurement range, a new phase unwrapping algorithm based on Three Wavelength Phase Shift Profilometry (TWPSP) is proposed in this paper. A series of fringe images only with three wavelengths λ1, λ2 and λ3, are captured by the 3D measurement system. Three equivalent wavelength sλ12, λ23 and λ123 based on the original three wavelengths are calculated to perform the phase unwrapping algorithm. Compared with the GC method, the proposed method can measure the objects with different colors under different illuminations. Compared with the MWPSP method, the proposed method is faster and high precision. Experiments demonstrate that the proposed method is robust, high precision, low noise and suit to measure the object with variety colors under different illumination. It can be used to measure arbitrary step height and multiple objects together.