A focus checking technique for image analysis systems

摘要

The paper describes a method of checking the accuracy of focus of images scanned with a raster scanner, by means of direct analysis of the data from a single scan. The parameter used is a measure of the high frequency response of the system to sharp edges in the image, and is obtained by comparing entries of tables of density differences between adjacent and near-adjacent pixels along scanlines. The technique has been incorporated into an autofocussing module of an automated cytology prescreening system, and has been found to give adequate warning of focus errors when scanning a wide range of normal and abnormal cytology specimens.