Fast and robust fringe projection profilometry for surface with hole discontinuities via backlighting

In fringe projection profilometry (FPP), objects with hole discontinuities can lead to shadows and even phase unwrapping morbidity. To solve this problem, we propose an enhanced FPP system by employing the backlighting technique in this paper. This method consists of shadow compensation (SC) and high dynamic range (HDR) imaging; the SC is implemented using the optimal mask, which is obtained by fusing two high-contrast images from different backlight intensities; the HDR imaging is performed by a multi-exposure technique to tackle the issue of multi-colored or specular reflections. Since the proposed method does not require complex phase-unwrapping algorithms, it is fast and robust for three-dimensional shape measurement of objects with hole discontinuities. To validate the method, morphological measurements of a wheel rim and a multi-colored human mask were performed. The results show that the proposed method can overcome discontinuity problems without degrading performance.

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