  It is a challenge for Phase Measurement Profilometry (PMP) to measure objects
with a large range of reflectivity variation across the surface. Saturated or
dark pixels in the deformed fringe patterns captured by the camera will lead to
phase fluctuations and errors. Jiang et al. proposed a high dynamic range
real-time 3D shape measurement method without changing camera exposures. Three
inverted phase-shifted fringe patterns are used to complement three regular
phase-shifted fringe patterns for phase retrieval when any of the regular
fringe patterns are saturated. But Jiang's method still has some drawbacks: (1)
The phases in saturated pixels are respectively estimated by different formulas
for different cases. It is shortage of an universal formula; (2) it cannot be
extended to four-step phase-shifting algorithm because inverted fringe patterns
are the repetition of regular fringe patterns; (3) only three unsaturated
intensity values at every pixel of fringe patterns are chosen for phase
demodulation, lying idle the other unsaturated ones. We proposed a method for
enhanced high dynamic range 3D shape measurement based on generalized
phase-shifting algorithm, which combines the complementary technique of
inverted and regular fringe patterns with generalized phase-shifting algorithm.
Firstly, two sets of complementary phase-shifted fringe patterns, namely
regular and inverted fringe patterns are projected and collected. Then all
unsaturated intensity values at the same camera pixel from two sets of fringe
patterns are selected, and employed to retrieve the phase by generalized
phase-shifting algorithm. Finally, simulations and experiments are conducted to
prove the validity of the proposed method. The results are analyzed and
compared with Jiang's method, which demonstrate that the proposed method not
only expands the scope of Jiang's method, but also improves the measurement
accuracy.
