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27 February 2015 An edge-from-focus approach to 3D inspection and metrology
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We propose an edge-based depth-from-focus technique for high-precision non-contact industrial inspection and metrology applications. In our system, an objective lens with a large numerical aperture is chosen to resolve the edge details of the measured object. By motorizing this imaging system, we capture the high-resolution edges within every narrow depth of field. We can therefore extend the measured range and keep a high resolution at the same time. Yet, on the surfaces with a large depth variation, a significant amount of data around each measured point are out of focus within the captured images. Then, it is difficult to extract the valuable information from these out-of-focus data due to the depth-variant blur. Moreover, these data impede the extraction of continuous contours for the measurement objects in high-level machine vision applications. The proposed approach however makes use of the out-of-focus data to synthesize a depth-invariant smoothed image, and then robustly locates the positions of high contrast edges based on non-maximum suppression and hysteresis thresholding. Furthermore, by focus analysis of both the in-focus and the out-of-focus data, we reconstruct the high-precision 3D edges for metrology applications.
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Fuqin Deng, Jia Chen, Jianyang Liu, Zhijun Zhang, Jiangwen Deng, Kenneth S. M. Fung, and Edmund Y. Lam "An edge-from-focus approach to 3D inspection and metrology", Proc. SPIE 9405, Image Processing: Machine Vision Applications VIII, 94050E (27 February 2015);

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