Another study systematically evaluated 13 autofocus functions for FISH
studies of counterstained nuclei [14]. Using a proposed figure-of-merit criterion
that weighs five different characteristics of an autofocus function, it reported
that functions based on correlation measures have the best performance for the
specific images studied.
The autofocus functions just mentioned can be categorized into methods
based on (1) edge strength, (2) contrast, (3) autocorrelation, and (4) the Fourier
spectrum of an image. Table 16.1 tabulates these functions along with their
definition and references. In this table the image is represented by g
i, j
, where
i and j are the spatial coordinates, g is the pixel intensity, G
x
and G
y
are the first-
order derivative of Gaussian ...