Comparison of digital focus criteria for a TV microscope system

Abstract

Existing focusing methods, such as standard deviation of gray values, gradients, information content of the image and the lateral inhibition function, were compared, and a new combination criterion was developed. This combined method consists of using the standard deviation of the image for coarse focusing followed by a modified form of the lateral inhibition for the fine focus. The lateral inhibitor model of the eye is a recursive filter that can be simplified to a nonrecursive filtering algorithm, as postulated by Rechenberg. The reported focus method operates over a focusing range (z‐axis) of ± 300 μm and is accurate within ±0.1 μm in the transmission, dark‐field, and phase contrast microscope. Copyright © 1984 Wiley‐Liss, Inc.