JPH0123828B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for optically identifying the authenticity of banknotes and the like.

BACKGROUND TECHNOLOGY Conventionally, for example, devices for optically identifying the authenticity of banknotes detect minute patterns on banknotes,
Authenticity has been determined by methods such as detecting the transmittance of specific parts. However, with the spread of copying materials in recent years, it has become easier to obtain duplicate counterfeit notes, and identification methods have also become more complex. An identification method based on a ratio of transmittance and a method based on a ratio of transmittance at two specific locations on a banknote using the same light source have been proposed.

Two types of ink are used in banknotes: special ink containing magnetic iron (hereinafter referred to as magnetic ink) and colored ink (hereinafter referred to as color ink). The proportion of ink mixture is related to the design and varies from place to place. For example, in the case of a 1,000 yen bill, there is a large amount of magnetic ink in the face area of the figure, but there is no magnetic ink in the area from the right side of the figure to the edge of the bill, which is all colored ink, The dark green areas, such as the shoulders of the statue, are between the two.

FIG. 1 shows an example of actual measurements of the spectral characteristics at the three locations mentioned above, where a indicates the color ink section, b indicates the dark green section, and c indicates the magnetic ink section.

As is well known, the spectral characteristics of a counterfeit note made in color copy are very similar to the spectral properties of the color ink part in Figure 1a, and the spectral properties of a counterfeit note made in black and white are very similar to the spectral properties of the magnetic ink part in Figure 1c. are doing. However, in the case of a counterfeit note made by ordinary copying, its spectral characteristics do not exhibit an intermediate value as shown in FIG. 1b.
Therefore, if a location such as the dark green area mentioned above is selected as the part to be inspected, it is possible to distinguish between authenticity and falsehood based on the difference in spectral characteristics.

In general, as shown in FIG. 2a, when a certain medium 1 is irradiated with light having an intensity of Ii, and the transmitted light obtained is Io, the following equation holds true according to Lambert's law.

Io＝Ii×10 ^- 〓 ^o

Claims (1)

[Claims] 1. By determining the ratio of absorbance to visible light and absorbance to infrared light at a predetermined location of a test object such as a banknote, and checking whether this absorbance ratio is within a predetermined range. , an optical identification method for banknotes, etc., characterized in that the authenticity of the test object, such as the banknote, is determined. 2. By taking the logarithm of the ratio of the transmitted light at the unprinted area of the test object such as a banknote, determined using the same light source, to the transmitted light at the predetermined inspection location, the absorbance at the above-mentioned predetermined inspection location can be calculated. 1. A method for optically identifying banknotes, etc., according to claim 1. 3 Banknotes, etc. are determined by checking whether the absorbance (or transmittance) of at least one of the absorbance (or transmittance) for visible light and the absorbance (or transmittance) for infrared light is within a predetermined range. An optical identification method for banknotes, etc., according to claims 1 and 2, for identifying authenticity of a test object.