Abstract: A color-sensitive currency verifier operating with a plurality of narrowband light sources optically coupled to a single broadband photodetector and including means for automatically balancing the color outputs of the various light sources. Color balancing is accomplished just prior to the examination of a specimen bill. The data samples are taken under the control of a microprocessor and used to authenticate the specimen bill both on the basis of pattern and color information stored in memory. Multiple data samples from a single target area are divided to compensate for soiling condition of the bill, and further compensation for condition of the bill is provided by adjusting the conversion scale factor of an A/D converter on the basis of data samples taken from a reference target area on the surface of the specimen bill before test or data samples are taken.