Diatom Autofocusing in Brightfield Microscopy: a Comparative Study

We present a number of autofocusing methods in lighting microscopy for its use in diatom identi cation. Among these, the Tenengrad method has been considered one of the best. The basic requirements for a practical autofocusing system are speed, sharpness and robustness to noise. Recently other focus measures based on a modi ed Laplacian method are said to perform better than Tenengrad. We investigate two sound methods based on a modi ed Tenengrad and a modied Laplacian. Measurements show that they provide a reliable and suitable focus measure that outperform similar methods. We investigate the window size analysis dependency and perform an univariate analysis on the focus measures. The focusing techniques are implemented in an automatic slide scanning system for diatom detection and identi cation for its use in the ADIAC project. 1