3D-profilometry of moving objects with abrupt surface discontinuities by projection of two-frequency color-coded fringe patterns

3D-profilometry of discontinuous solids by fringe projection is a difficult task due to the problem posed by the phase (profile) unwrapping at sharp borders. To solve this problem, Servin et al. proposed the so-called two-steps temporal unwrapping, in which two consecutive sequences of fringe patterns with different spatial frequencies (a low- and a high-frequency patterns sequence) are projected over a static test surface. As the 3D surface profile is retrieved by phaseshifting techniques, each fringe sequence must have at least three phase-shifted frames, which in principle would preclude the use of temporal unwrapping for measuring moving objects since at least it would be necessary to acquire a total of twelve frames (six frames for the test object plus six more for a reference plane). In the present work we present an improvement to this method, which requires the acquisition of only two color-coded fringe patterns (i.e., two RGB-images) for reconstructing the discontinuous 3D surface of a moving object. The proposed approach is based on the projection of fringes with two different frequencies. Validation experiments are presented.