Fourier analysis of RGB fringe-projection profilometry and robust phase-demodulation methods against crosstalk distortion

摘要

In this paper we apply the frequency transfer function (FTF) formalism toanalyze the red, green and blue (RGB) phase-shifting fringe-projectionprofilometry technique. The phase-shifted fringe patterns in RGB fringeprojection are typically corrupted by crosstalk because the sensitivity curvesof most projection-recording systems overlap. Crosstalk distortion needs to becompensated in order to obtain high quality measurements. We studyphase-demodulation methods for null/mild, moderate, and severe levels of RGBcrosstalk. For null/mild crosstalk, we can estimate the searched phase-mapusing Bruning's 3-step phase-shifting algorithm (PSA). For moderate crosstalk,the RGB recorded data is usually preprocessed before feeding it into Bruning'sPSA; alternatively, in this paper we propose a computationally more efficientapproach, which combines crosstalk compensation and phase-demodulation into asingle process. For severe RGB crosstalk, we expect non-sinusoidal fringes'profiles (distorting harmonics) and significant uncertainties on the crosstalkcalibration (which produces pseudo-detuning error). Analyzing these distortingphenomena, we conclude that squeezing interferometry is the most robustdemodulation method for RGB fringe-projection techniques. We support ourconclusions with numerical simulations and experimental results.