The accuracy of face recognition systems is significantly affected by the quality of face sample images. Using degraded face sample images can significantly decrease the performance of face recognition systems. There are not many face quality enhancement methods in the research field. Therefore, it is interesting to investigate whether existing image quality enhancement methods can improve the performance of biometric systems for degraded face images. In this paper, we conduct an experiment to apply nine image enhancement methods to a face database, which contains high quality and degraded face sample images. The experimental results show that some of selected enhancement methods can improve face recognition system performance.
The shrinking generator is a popular representation of pseudorandom sequence generators (PRSGs) that employ so-called irregular clocking. This familiy of PRSGs is characterized by having one or more linear feedback shift registers (LFSRs), whose clocking is controlled by the output sequence of one of the subgenerators. Such a sequence is called clock-control sequence. In this thesis, an algorithm is presented that reconstructs the clock-control sequence in the generalized shrinking generator in the presence of noise. The shrinking generator is first reduced to a step1-stepE generator (another class of PRSGs with irregular clocking), where E depends on the maximum length of runs of zeros in the output sequence of the clocking part of the generator. Then a directed depth-first like search for optimal and suboptimal paths in the edit distance matrix corresponding to the generator is performed. The permitted path weight deviation from the optimum is determined by the noise level in the statistical model of the generator. Influence of inadequate estimation of the length of the output sequence of the clocked LFSR without irregular clocking on the level of equivalent noise is discussed. The experimental results that are presented show that the total number of candidate clock-control sequences increases moderately as the necessary clock-control sequence length increases. The advantage of this attack over the other attacks reported in the litterature is that this attack is effective even if the noise level is relatively high and that the solution is guaranteed to
