Topological coding of single fingerprints

The motivation for seeking topological descriptions of single fingerprints is provided by the elasticity of the human skin; successive impressions from the same finger will in-variably have suffered a degree of relative distortion (translation, rotation and stretching). Topology based systems should be free from the detrimental effects of plastic distortion. This thesis is divided into three parts: part I outlines the traditional use of fingerprints as a basis for personal identification and gives detailed explanation of the arguments in favour of topological coding. Methods for the extraction of topology based digital codes are suggested and the ‘placing of lines’ is introduced as an effective means of ordering topological information. In part II specific systems are described for the extraction of simple topological codes from rolled impressions of the pattern types ‘ loops’ , ‘whorls’ and ‘arches’ . The generated codes take the form of vectors or simple digital arrays. The nature and frequency of changes that may occur in such codes is investigated and fingerprint comparison algorithms, based on these topological codes, are developed. The objective of such algorithms is to draw a score derived from the degree of ‘nearness’ of the topological codes in such a manner that it intelligently reflects similarity or dissimilarity in the two prints under comparison. Part III examines the special problems relating to fragmentary ‘scenes-of-crime’ marks. It describes methods of coding fingerprint patterns by a variety of ‘topological coordinate schemes’ , with fingerprint comparison being performed on the basis of localised topological information which is extracted from the recorded coordinate sets. Furthermore, a method for pictorial reconstruction of a complete fingerprint, from its coordinate representation, is demonstrated. Comparison of fingerprints on the basis of digital topological descriptions is shown to offer a substantial improvement in performance over existing (spatial) techniques.