3-D Shape Measurement of Translucent Objects Based on Fringe Projection

Fringe projection profilometry (FPP) has been widely used in various fields because of its advantages of noncontact, nondestructive, high precision, and high speed. However, due to the subsurface scattering effect, FPP encounters severe challenges when performing 3-D measurements of translucent objects. Based on FPP, this article proposes a novel 3-D measurement method for translucent objects using periodic line-fringe patterns and complementary Gray code patterns. By photographing a set of periodic line-fringe patterns with different phases and performing multi-Gaussian sum fitting on the grayscale values of the same pixel position in different images, the wrapping phase of the fringe corresponding to the maximum fit grayscale value can be obtained. Furthermore, a novel complementary Gray code method is proposed to solve the absolute phase, which avoids phase unwrapping errors caused by subsurface scattering. Comparative experimental results show that the point cloud of translucent objects obtained using the proposed 3-D reconstruction method is more complete, denser, and smoother, and more accurate. The fitting diameter errors of the reconstruction results of the translucent nylon sphere and polypropylene (PP) sphere are 0.025 and 0.044 mm, respectively. In addition, our method can use the conventional binocular stereo vision system based on grating projection, without modifying the hardware system.