Adaptive particle image velocimetry based on sharpness metrics M. Teich, J. Grottke, H. Radner, L. Büttner and J. W. Czarske J. Eur. Opt. Soc.-Rapid Publ., 14 1 (2018) 5 Published online: 20 February 2018 DOI: 10.1186/s41476-018-0073-0