Matching of partial fingerprints has important applications in both biometrics and forensics. It is well-known that
the accuracy of minutiae-based matching algorithms dramatically decrease as the number of available minutiae
decreases. When singular structures such as core and delta are unavailable, general ridges can be utilized. Some
existing highly accurate minutiae matchers do use local ridge similarity for fingerprint alignment. However, ridges
cover relatively larger regions, and therefore ridge similarity models are sensitive to non-linear deformation. An
algorithm is proposed here to utilize ridges more effectively- by utilizing representative ridge points. These points
are represented similar to minutiae and used together with minutiae in existing minutiae matchers with simple
modification. Algorithm effectiveness is demonstrated using both full and partial fingerprints. The performance
is compared against two minutiae-only matchers (Bozorth and k-minutiae). Effectiveness with full fingerprint
matching is demonstrated using the four databases of FVC2002- where the error rate decreases by 0.2-0.7% using
the best matching algorithm. The effectiveness is more significant in the case of partial fingerprint matching-
which is demonstrated with sixty partial fingerprint databases generated from FVC2002 (with five levels of numbers
of minutiae available). When only 15 minutiae are available the error rate decreases 5-7.5%. Thus the method,
which involves selecting representative ridge points, minutiae matcher modification, and a group of minutiae
matchers, demonstrates improved performance on full and especially partial fingerprint matching.
The fingerprint verification task answers the question of whether or not two fingerprints belongs to the same finger. The paper focuses on the classification aspect of fingerprint verification. Classification is the third and final step after after the two earlier steps of feature extraction, where a known set of features (minutiae points) have been extracted from each fingerprint, and scoring, where a matcher has determined a degree of match between the two sets of features. Since this is a binary classification problem involving a single variable, the commonly used threshold method is related to the so-called receiver operating characteristics (ROC). In the ROC approach the optimal threshold on the score is determined so as to determine match or non-match. Such a method works well when there is a well-registered fingerprint image. On the other hand more sophisticated methods are needed when there exists a partial imprint of a finger- as in the case of latent prints in forensics or due to limitations of the biometric device. In such situations it is useful to consider classification methods based on computing the likelihood ratio of match/non-match. Such methods are commonly used in some biometric and forensic domains such as speaker verification where there is a much higher degree of uncertainty. This paper compares the two approaches empirically for the fingerprint classification task when the number of available minutiae are varied. In both ROC-based and likelihood ratio methods, learning is from a general population of ensemble of pairs, each of which is labeled as being from the same finger or from different fingers. In the ROC-based method the best operating point is derived from the ROC curve. In the likelihood method the distributions of same finger and different finger scores are modeled using Gaussian and Gamma distributions. The performances of the two methods are compared for varying numbers of minutiae points available. Results show that the likelihood method performs better than the ROC-based method when fewer minutiae points are available. Both methods converge to the same accuracy as more minutiae points are available.
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