Digital multiple wavelength phase shifting algorithm

This paper presents a digital multiple-wavelength phase-shifting technique for three-dimensional shape measurement. The projected phase-shifted fringe images have wavelengths of λκ = W/2κ-1 (k = 1,2,3...). The phase unwrapping is not needed for the longest wavelength because a single fringe covers the whole area. The shorter wavelength phase, φκ(x,y), is unwrapped by referring to the previously unwrapped longer wavelength phase, Φk-1(x,y), pixel by pixel without accessing its neighborhood pixels. Experiments demonstrate that this technique has low noise and less sensitivity to motion. It can be used to measure arbitrary step height and multiple objects simultaneously.