Image analysis – Histogram processing – For setting a threshold
Patent
1992-03-03
1994-11-22
Couso, Yon J.
Image analysis
Histogram processing
For setting a threshold
382 17, G06K 900
Patent
active
053675770
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a method and a meals for optical testing of genuineness of bank notes, forms, cheques and similar paper bills. In particular the invention relates to recognizing paper notes on the basis of the particular optical signature of a genuine multilayer colour printed paper note, as opposed to the signature of a counterfeit note which hits been produced by means of a modern colour copying machine.
Until to-day, "good" forgeries of bank notes have been made by offset printing. It is just recently that colour copying machines have been enabled to copy bank notes with a passable result. Such modern colour copying machines are now entering the market, and banks are presented with a possibly very large problem with good colour copies of bank notes, cheques etc.
Previously a genuineness test of bank notes has usually been made by analysing embedded security parameters, like e.g. security thread and water mark. However, an automatic reading of e.g. a water mark is very difficult technically, ant also rather expensive. Thus, an authenticity test by means of these security parameters is adapted to a relatively small volume of test machines.
However, to-day quite a different volume of counterfeit bank notes is to be expected. One is in fact now confronted with a rather different type of counterfeiter than previously. "Amateurs" who to-day have access to a colour copying machine, will possibly flood the market with forged copies in a short time. Thus, it is reasonable to suppose that the largest part of counterfeit bank notes in the market in the time to come will be such copies from commercially accessable colour copying machines.
There is clearly a need of a cheap and rapid way of sorting out these colour copies. The present invention concerns a simple, cheap and above all very rapid method for sorting colour copies from genuine paper notes.
A genuine bank note is printed in a multilayer printing process, e.g. steel gravure or rotogravure. However, colour copying machines operate in a quite different manner, and they use quite different dye stuffs, with optical characteristics which are quite different from offset or steel gravure dye stuffs. The invention is intended to expose these differences in production method and dye material in the bank note printing process.
At this point it is opportune to mention briefly previously known and related optical methods:
An analysis of bank notes can of course be made by means of a scanning spectrophotometer, which exposes completely the optical signature all over the wavelength range in question, e.g. the range corresponding to visible light. Such a measuring technique, which of course is able to distinguish between colour copies and genuine bills, is quite useless in the practical case, due to the time required for testing one single bill.
However, there are numerous bank note receivers in the market to-day, which in addition to other tests also take a look at the bank note colours. But many of the methods used are limited to using only one colour. In the prior art it is usual to transport the bank note past one single colour sensor, and then the signal which appears is analysed along the length of the bill. Still, this technique works poorly, because the sensor is very sensitive to impurities and wear of the bank notes, as well as variations in the printing process of the genuine bank notes.
An improved method is disclosed in British patent application, publication no. 2,107,911, in which a bank note is scanned by a combination of two sensors respectively measuring in a green and a red colour range. The ratio between the measured intensities in red and green are formed, and the complete scanned track on the bank note is compared with a previously learned track. In this publication light emitting diodes are used as light sources, which gives a very limited choice of colours. Nor do ordinary light emitting diodes ever radiate with a constant intensity, and this means that the disclosed system has a very limited precision and stability.
Also U.S. Pat.
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Couso Yon J.
Datalab Oy
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