Automatic exposure control method for 3D shape measurement of specular surface based on digital fringe projection

Abstract

Digital fringe projection is widely used in three-dimensional (3D) shape measurement. However, its performance is severely disturbed when measuring complex surfaces with a wide range of reflectivity. In this paper, to enhance the underexposed regions and reduce the saturated regions, an automatic and effective method is proposed for the multi-exposure determination of digital fringe projection (DFP) system. During the whole process, only one unsaturated image needs to be captured preliminarily, which could establish an adaptive strategy based on the intensity value distribution function. The raw absolute phase maps captured with different exposure times are synthesized at pixel level for phase retrieval and 3D reconstruction. To evaluate the effectiveness of our method, the high dynamic range (HDR) method and global optimal exposure (GOE) method are introduced for comparison. Verification experiments show that our method performs better for the 3D reconstruction results of the complex surface with a large reflectivity range.