A contrast-based focusing criterium

In this paper a new criterion for determining the optimal focus setting during the image acquisition process is presented. It is based upon a new representation of the focal variation of contrast between images: the dynamic contrast histogram (DCH). The DCH of a point is a scaled joint probability density function between the gray levels of two images of the same scene, acquired with different focus settings in a neighbourhood of that point. The dynamic focusing criterion (DFC) developed here computes the slope of the principal axis of the DCH as a focusing criterion. The results of this technique are compared to other methods based on a quality measure of its focusing ability, its sensitivity to noise, and its computational complexity. Results are presented from microscopic images.