Multifrequency grating projection profilometry based on the nonlinear excess fraction method.

Although promised to be a fast and accurate three-dimensional shape measurement technique, grating projection profilometry based on phase measurement has been frequently baffled by the difficulty in phase unwrapping. We introduce the conventional excess fraction method into profilometry and extend it to nonlinear domain. Nonlinear excess fraction method (NLEFM), on the basis of which a multifrequency grating projection profilometry is developed, can work as a robust temporal phase unwrapper, which may extend the reliable measuring range by dozens of times at no cost of accuracy. The principle of NLEFM is detailed, and experimental results are given in which complex profiles are reliably measured with the novel system.