First, a novel approach to the binarization of the curves and grids in the water level sheet image has been proposed, which is based on the fusion of gradient and color information adaptively. Second, a fast search strategy for cross point location is invented and point-by-point processing is thus avoided, with the help of grid distribution information. And finally, we put forward a local rectification method through analyzing the central portions of the image and utilizing the domain knowledge of hydrology. The processing speed is accelerated, while the accuracy is still satisfying. Experiments on several real water level records show that our proposed techniques are effective and capable of recovering the hydrological observations accurately.
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Shijin Li, Di Zhan, Jinlong Hu, Xiangtao Gao, Ping Bo, "Study on key techniques for camera-based hydrological record image digitization," Proc. SPIE 9675, AOPC 2015: Image Processing and Analysis, 967511 (8 October 2015);