Accurate determination of singular points and principal axes on a fingerprint

The accuracy of the location of singular points on a fingerprint is important for the Poincare index to correctly determine the type of singular points: ordinary, delta, core or double-core. In this paper, we present a novel yet simple and accurate technique for the automatic determination of singular points. The technique offers a double-resolution estimation of the ridge orientation on a 4×4-pixel quincunx grid and quantises ridge orientations into six codes called ridge flow codes. Singular regions are defined as where all six codes exist. A singular point within a singular region can then be quickly determined by locating the point where the variance of local ridge orientation is at its maximum. The distribution and type of the singular points, together with their associated principal axes, may then be used to classify a fingerprint into one of six well-known classes or patterns.