On the Use of Log-Likelihood Ratio Based Model-Specific Score Normalisation in Biometric Authentication

  • Norman Poh
  • Josef Kittler
Part of the Lecture Notes in Computer Science book series (LNCS, volume 4642)


It has been shown that the authentication performance of a biometric system is dependent on the models/templates specific to a user. As a result, some users may be more easily recognised or impersonated than others. We propose a model-specific (or user-specific) likelihood based score normalisation procedure that can reduce this dependency. While in its original form, such an approach is not feasible due to the paucity of data, especially of the genuine users, we stabilise the estimates of local model parameters with help of the user-independent (hence global) parameters. The proposed approach is shown to perform better than the existing known score normalisation procedures, e.g., the Z-, F- and EER-norms, in the majority of experiments carried out on the XM2VTS database . While these existing procedures are linear functions, the proposed likelihood based approach is quadratic but its complexity is further limited by a set of constraints balancing the contributions of the local and the global parameters, which are crucial to guarantee good generalisation performance.


Gaussian Mixture Model Equal Error Rate Biometric System False Acceptance Rate False Rejection Rate 
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Copyright information

© Springer-Verlag Berlin Heidelberg 2007

Authors and Affiliations

  • Norman Poh
    • 1
  • Josef Kittler
    • 1
  1. 1.CVSSP, University of Surrey, Guildford, GU2 7XH, SurreyUK

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