A novel approach to obtain optimal exposure for 3D shape reconstruction of high dynamic range objects

Abstract

The approach to choose the exposure sequence substantially affects the performance of the multiexposure structured light method when reconstructing the 3D shape of high dynamic range (HDR) targets. Previous researchers have conducted numerous works regarding how to select exposure time automatically, but most of them lack the consideration of the time efficiency of the 3D measurement when selecting the exposure time. In this paper, a novel approach to obtain optimal exposure for HDR targets is proposed. We developed a concept, namely, exposure style, to help us find the optimal exposure sequence. The area-weighted method is proposed as a guide to find the preliminary exposure sequence with the demanded exposure style. By uniform sampling, the preliminary exposure sequence is sampled into several alternate sequences with different lengths. By utilizing the exposure fusion method, the fused images generated by the captured images, which is under the exposures of these alternate sequences, are used to reconstruct the 3D shape of the HDR target. Then, the running time of 3D measurement and the number of generated 3D cloud points are recorded. By evaluating these two indicators comprehensively, the time efficiency of the selected exposure sequence is well-considered, and the sequence with the highest score is selected as the final optimal exposure sequence. Three HDR targets with different grayscale distributions are chosen to testify to the practicability of our method. The auto-HDR method and Zhang’s method are introduced for comparison. The experimental results show that the optimal exposure sequence selected by our auto-exposure strategy performs better than other methods and the 3D shape of HDR targets can be reconstructed completely and accurately.