| CPC G07D 7/1205 (2017.05) [G07D 7/2008 (2013.01)] | 15 Claims |
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1. A sensor for checking value documents, in particular banknotes, each having a luminescent sheet-like substrate and a luminescent feature applied to a partial surface of the substrate, comprising:
a detection device which is configured to detect luminescence radiation emitted by a value document to be checked in at least two different spectral ranges in a spatially resolved manner,
wherein a plurality of measurement points is obtained, to each of which a spectral vector is assigned which contains at least two intensity values which characterize the intensity of the luminescence radiation detected at the respective measurement point in the at least two spectral ranges, and
an evaluation device which is configured
a) to determine, for each of a plurality of measurement points, a substrate intensity value and a feature intensity value from the spectral vectors using a predetermined substrate basis vector and a predetermined feature basis vector, the substrate basis vector and the feature basis vector each having at least two intensity values, which characterize the expected intensity of the luminescence radiation emitted by the substrate or feature, respectively, in the at least two spectral regions,
b) to determine, on the basis of the substrate intensity values and feature intensity values, a pure substrate mask which contains those measurement points which correspond to locations on the value document which lie outside the feature, and
c1) to determine, from the spectral vectors of the measurement points contained in the pure substrate mask, a mean substrate vector which contains at least two intensity values which are obtained in each case by combining, in particular by averaging or quantile formation, the intensity values contained in the spectral vectors for each of the at least two spectral ranges, and
i) to determine, for each of a plurality of measurement points, a corrected feature intensity value and/or a corrected substrate intensity value from the spectral vectors using the mean substrate vector, and/or
ii) to determine a spectral signature of the substrate and/or a spectral signature of the feature, by which a spectral composition of the luminescence radiation emitted by the substrate or the feature, respectively, is characterized, using the mean substrate vector, and/or
c2) to determine a temporal behavior of the luminescence radiation emitted by the substrate and/or the feature using measurement points contained in the pure substrate mask, and
d) to check, in particular with regard to authenticity, the value document on the basis of the corrected feature intensity values and/or on the basis of the corrected substrate intensity values and/or on the basis of the spectral signature of the substrate and/or of the feature and/or on the basis of the temporal behavior of the luminescence radiation emitted by the substrate and/or by the feature.
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