Derivative-based image quality measure for autofocus in electron microscopy

Automatic focusing methods are based on an image quality measure, which is a realvalued estimation of an image’s sharpness. In this paper we study L_1- or L_2-norm derivative-based image quality measures. For a bench mark case these measures turn out to be quadratic, which implies that after obtaining of at least three images one can find the position of the optimal defocus. The resulting autofocus method is demonstrated for a reference scanning transmission electron microscopy application. Keywords: Electron microscopy · Autofocus · Linear image formation · Image quality measure.