Time-slicing high dynamic range 3D imaging.

Fringe projection profilometry (FPP) has been widely used in 3D measurement due to its high precision and non-contact properties. Nevertheless, it still faces great challenges in measuring scenes with complex reflectivity, in which the dynamic range of the reflected light field of the scene is significantly higher than that of the image detector. In this paper, we propose a time-slicing strategy for high dynamics range 3D imaging by projecting a series of sinusoidal fringe patterns with short and equal length exposure time and performing the fusion of different numbers of short exposure images according to the local gray-value distribution of the images. Moreover, to further improve the measurement efficiency, we realize phase unwrapping using complementary Gray code patterns, which are binary and insensitive to the image sensor's nonlinear response to the reflected light from the scene under test. Experiments are conducted to demonstrate the feasibility and efficiency of the proposed method.

Projected feature assisted coarse to fine point cloud registration method for large-size 3D measurement.

Fringe projection profilometry has gained significant interest due to its high precision, enhanced resolution, and simplified design. Typically, the spatial and perspective measurement capability is restricted by the lenses of the camera and projector in accordance with the principles of geometric optics. Therefore, large-size object measurement requires data acquisition from multiple perspectives, followed by point cloud splicing. Current point cloud registration methods usually rely on 2D feature textures, 3D structural elements, or supplementary tools, which will increase costs or limit the scope of the application. To address large-size 3D measurement more efficiently, we propose a low-cost and feasible method that combines active projection textures, color channel multiplexing, image feature matching and coarse-to-fine point registration strategies. Using a composite structured light with red speckle patterns for larger areas and blue sinusoidal fringe patterns for smaller ones, projected onto the surface, which allows us to accomplish simultaneous 3D reconstruction and point cloud registration. Experimental results demonstrate that the proposed method is effective for the 3D measurement of large-size and weak-textured objects.

Fast fringe projection profilometry using 3 + 1 phase retrieval strategy and fringe order correction.

Fringe projection profilometry (FPP) has attracted wide attention in optical 3D measurement field for its high resolution, high accuracy, and simple system construction. However, the inherent requirements of FPP's measurement speed and accuracy are contradictory. We adopt a 3+1 phase retrieval strategy combining phase shift and the Hilbert transform algorithm to achieve high-speed, high-precision simultaneous measurements with only four binary fringe patterns. Furthermore, when using temporal phase unwrapping, fringe order errors (FOEs) are inevitable. Although these FOEs do not affect neighboring pixels, they are brought into the final point cloud coordinates by the absolute phase value. We propose a fringe order correction method to eliminate FOEs. The feasibility and effectiveness of this method are verified by the experimental results.