Previous works show that the fact that a paper surface is non-uniform can be used in paper artifact-metrics. By scanning the paper surface with a high-resolution scanner, the study on paper artifact-metrics is reduced to the study on image pattern matching. Unlike usual image pattern matching, few feature points exists. In previous works, a correlation coefficient of two scanned images is used as a similarity of them. For the number of pixels TV, the complexity of this method is O(N). This paper proposes a new discriminant function in O(N~(1/2) logN~(1/2)) that is based a phase only correlation.
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