Dynamic 3D measurement of thermal deformation based on geometric-constrained stereo-matching with a stereo microscopic system

In three-dimensional (3D) shape measurement applications based on absolute phase matching in fringe projection profilometry, measurement accuracy can be improved by using denser fringes under the pre-condition that the phase ambiguities can be successfully removed after phase unwrapping. In real-time measurement situations, the number of fringe patterns is limited to reduce motion-induced errors, which does, however, pose more difficulties for the absolute phase recovery of dense fringes. In this paper, we propose a stereo phase matching method that takes advantage of the high accuracy of denser fringes and the high efficiency of using only two different fringe frequencies. The phase map is divided into several subareas, and in each sub-area the phase is unwrapped independently. The stereo-matched pixel is selected from the distributed candidates in these sub-areas by geometric constraints. Experimental results show that only five patterns are needed to perform a high-accuracy real-time 3D measurement of the thermally induced deformation of the sample under different heating temperatures based on a telecentric stereo microscopic system.