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A newly developed flexible calibration algorithm for telecentric 3D measurement systems is presented in this paper. We theoretically analyzed the similarities and differences between the telecentric and entocentric system. The telecentric system can be calibrated with the aid of the traditional 2D planar calibration method. An additional two-step refining process is proposed to improve the calibration accuracy effectively. With the calibration and refining algorithm, an affine camera can be calibrated with a reprojection error of 0.07 pixel. A projector with small field of view (FOV) is applied to achieve a full 3D reconstruction in our profilometry system. Experiments with a prototype demonstrate the validation and accuracy of the proposed calibration algorithm and system configuration. The reconstruction accuracy can achieve 5 µm with a measurement FOV of 28.43 mm×21.33 mm and a working distance of 110 mm.

We introduce a flexible error correction method for fringe projection profilometry (FPP) systems in the presence of local blur phenomenon. Local blur caused by global light transport such as camera defocus, projector defocus, and subsurface scattering will cause significant systematic errors in FPP systems. Previous methods, which adopt high-frequency patterns to separate the direct and global components, fail when the global light phenomenon occurs locally. In this paper, the influence of local blur on phase quality is thoroughly analyzed, and a concise error correction method is proposed to compensate the phase errors. For defocus phenomenon, this method can be directly applied. With the aid of spatially varying point spread functions and local frontal plane assumption, experiments show that the proposed method can effectively alleviate the system errors and improve the final reconstruction accuracy in various scenes. For a subsurface scattering scenario, if the translucent object is dominated by multiple scattering, the proposed method can also be applied to correct systematic errors once the bidirectional scattering-surface reflectance distribution function of the object material is measured.

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