  In this paper we apply the frequency transfer function (FTF) formalism to
analyze the red, green and blue (RGB) phase-shifting fringe-projection
profilometry technique. The phase-shifted fringe patterns in RGB fringe
projection are typically corrupted by crosstalk because the sensitivity curves
of most projection-recording systems overlap. Crosstalk distortion needs to be
compensated in order to obtain high quality measurements. We study
phase-demodulation methods for null/mild, moderate, and severe levels of RGB
crosstalk. For null/mild crosstalk, we can estimate the searched phase-map
using Bruning's 3-step phase-shifting algorithm (PSA). For moderate crosstalk,
the RGB recorded data is usually preprocessed before feeding it into Bruning's
PSA; alternatively, in this paper we propose a computationally more efficient
approach, which combines crosstalk compensation and phase-demodulation into a
single process. For severe RGB crosstalk, we expect non-sinusoidal fringes'
profiles (distorting harmonics) and significant uncertainties on the crosstalk
calibration (which produces pseudo-detuning error). Analyzing these distorting
phenomena, we conclude that squeezing interferometry is the most robust
demodulation method for RGB fringe-projection techniques. We support our
conclusions with numerical simulations and experimental results.
