One-shot dual-projection topography enhanced by phase-shifting logical moiré

In conventional dual-projection moiré topography, the additive-type moiré pattern has an amplitude modulated form, and therefore poor visibility, unable to be improved through low-pass filtering. To overcome this difficulty, this paper presents an enhanced dual-projection moiré topography by means of logical moiré. In its implementation, a couple of projectors project two fringe patterns of different colors onto the object simultaneously and then a color camera captures the deformed fringe pattern. Instead of directly processing the additive-type moiré fringes, we separate the deformed fringes of two chromatic channels, binarize them, and then calculate their exclusive OR (XOR) moiré pattern. By differentiating one of the two deformed fringe patterns, a second XOR moiré pattern having exactly a π/2-rad phase shift can also be generated, so that the phases are simply calculated by using an arctangent function after low-pass filtering to the XOR moiré patterns. By doing so, we can measure the three-dimensional shape of an object in an efficient way requiring a single-shot implementation. The validity of this method has been demonstrated through simulation and experimental results.