The Importance of Small Pupils: A Study of How Pupil Dilation Affects Iris Biometrics

This work studies the effect of pupil dilation on the accuracy of iris biometrics. We find that when matching enrollment and recognition images of the same person, larger differences in pupil dilation yield higher template dissimilarities, and so a greater chance of a false non-match. Another experimental result is that even when the degree of dilation is similar at enrollment and recognition, comparisons involving highly dilated pupils result in worse recognition performance than comparisons involving constricted pupils. We find that when the matched images have similarly highly dilated pupils, the mean Hamming distance of the match distribution increases and the mean Hamming distance of the non-match distribution decreases, bringing the distributions closer together from both directions. We recommend that a measure of pupil dilation be kept as meta-data for every iris code. Also, the absolute dilation of the two images, and the dilation difference between them, should factor into a confidence measure for an iris match.