RESUMO
Fringe projection profilometry (FPP) has been widely used for three-dimensional shape measurement because of its simple hardware and high measurement accuracy. However, the use of most FPP systems to measure complex surfaces such as stepped height objects can result in severe occlusion and shadow. To alleviate this problem, a coaxial measurement method based on dual biprisms is presented in this paper. The system is low-cost and easy to implement, and does not require the introduction of mechanical moving parts. Only dual biprisms are introduced into the coaxial system to provide the geometric constraints required for reconstruction. Experimental results on the reconstruction of a surface with significant height changes demonstrate that the proposed method can achieve shadow-free measurements.
RESUMO
Intensity-based fringe projection profilometry (IBFPP) is used widely because of its simple structure, high robustness, and noise resilience. Most IBFPP methods assume that any scene point is illuminated by direct illumination only, but global illumination effects introduce strong biases in the reconstruction result for many real-world scenes. To solve this problem, this paper describes an efficient IBFPP method for reconstructing three-dimensional geometry in the presence of global illumination. First, the average intensity of two sinusoidal patterns is used as a pixel-wise threshold to binarize the codeword patterns. The binarized template pattern is then used to convert other binarized fringe patterns into traditional Gray-code patterns. A proprietary compensation algorithm is then applied to eliminate fringe errors caused by environmental noise and lens defocusing. Finally, simple, efficient, and robust phase unwrapping can be achieved despite the effects of subsurface scattering and interreflection. Experimental results obtained in different environments show that the proposed method can obtain three-dimensional information reliably when influenced by global illumination.