Estimating Image Focusing in Fingerprint Scanners

This work is motivated by the need of simple and practical techniques to evaluate fingerprint scanners for non-AFIS applications. One of the characteristics that has to be considered for the evaluation of a fingerprint scanner is the capability of providing well focused images. It is common practice to indirectly estimate this characteristic by measuring the scanner modulation transfer function (MTF). Unfortunately this requires a rather complex setup and specific expensive targets. In this paper a novel index (TSI) is proposed to simply evaluate finger image focusing. The method is based on the measurement of the steepness of the ridge/valley transitions of the fingerprint impressions. The experimental results confirm the strict relation between the proposed index and the ability of a scanner to clearly focus the fingerprint.