Double-shot N-step phase measuring profilometry

Recently, a single-shot N-step phase measuring profilometry was proposed by our research group. It not only maintains the single-shot real-time measuring characteristics but also makes its measuring accuracy selectable as appropriate N. But when the spectral aliasing in the captured deformed pattern is severe, the alternative current (AC) component may be extracted imprecisely or even failed. So, a double-shot N-step phase measuring profilometry (double-shot N-PMP) is proposed. While two complementary sinusoidal gratings are projected onto the measured object, the AC component of the captured deformed patterns can be extracted precisely even if spectrum aliasing is very serious. If the AC component multiplies with N frames of the AC components of the N-step phase-shifting fringe patterns captured from the reference plane in advance, a new N-step phase-shifting algorithm for the phase difference between the measured object and the reference plane is accomplished to reconstruct the measured object. The experimental results show the possibility and effectiveness of the proposed method. It can either improve the measuring accuracy or expand application scope. Though the double-frame gratings are needed, the real-time measuring characteristics can still maintain with the time-division multiplexing method.