Image analysis – Histogram processing – For setting a threshold
Patent
1987-11-27
1990-12-11
Moore, David K.
Image analysis
Histogram processing
For setting a threshold
382 2, 356 71, 350358, G06K 900
Patent
active
049776010
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a method of recognizing fingerprints and similar skin surface structures in which the structure of a finger placed on a smooth surface is scanned and compared with a structure stored on a record carrier. The invention further relates to a system for carrying out such a method.
STATE OF THE ART
Devices for recognizing fingerprints are already known or have already been proposed in various forms. Thus, for example systems exist in which the fingerprint characteristics once detected are stored in a central computer from which the characteristics can be called up when required for comparison with the actual fingerprint which is obtained by a detection or scanning device. Such systems may however meet with objections for data protection reasons. For this reason systems have also been developed in which the characteristics of a fingerprint are recorded in a sort of identification card which the proprietor of the card himself inserts into a recognition device directly for comparison with his corresponding finger.
The comparison is carried out in the known systems in various manners. Thus, purely electronic methods are known as well as methods based mainly on optical scanning with only the final comparison of the data being made electronically. In purely electronic detection methods the scanning of the fingerprint can for example be carried out by capacitive or other correspondingly small sensors disposed in a matrix form. For optical detection prisms can be used against which the surface of the finger is pressed. In this case for example the prism surface changes its reflection behaviour at the areas at which the adjacent medium is no longer air but the raised areas of the finger surface bearing on the prism surface.
All these devices have the common disadvantage that they are relatively complicated in construction and thus cannot be built in simple forms which could be incorporated in mass production into small detection or scanning devices. A great number of these relatively complicated and thus also relatively exact detection devices can easily be connected to a data processing and data acquisition system. This advantage is however only necessary in specific cases and as already mentioned above the central acquisition of fingerprint data may meet with objections on the basis of the data protection laws.
EXPLANATION OF THE INVENTION
The invention is based on the problem of providing a method and a corresponding system for detecting fingerprints which permit simple construction so that a device made on the basis thereof can be made so that it is simple and reliable in its operation and economical to make and consequently can be used at any desired location independently of data processing systems. The important aspect is not to be the highest possible detection accuracy; on the contrary, a certain error frequency rate is admissible because a chance incorrect recognition need not necessarily involve direct disadvantageous consequences to the person allowing his finger to be compared with a data carrier. The error frequency rate can possibly be reduced in that several detection or scanning operations are admissible consecutively and it is thus sufficient for only the last such operation to be successful.
This problem is solved according to the invention by the method according to the characterizing clause of claim 1.
By using ultrasonic waves compared with light waves the following advantages are achieved in fingerprint recognition:
1. The fact that sound travels about five times slower in air than in water, to which substantially most parts of the human body also correspond, and that moreover no difficulties are involved in finding for the application or support plate for the finger a material which has similar sound propagation properties to water, makes it possible to achieve that at the transition point of the skin and application surface the soundwaves can readily pass with substantially the same velocity through the areas at which the raised areas of the skin o
REFERENCES:
patent: 3614737 (1971-10-01), Sadowsky
patent: 4053228 (1977-10-01), Schiller
patent: 4385831 (1983-05-01), Ruell
patent: 4631965 (1986-12-01), De Vadder et al.
patent: 4785667 (1988-11-01), Miyajima et al.
patent: 4876725 (1989-10-01), Tomko
Proceedings of the IEEE, Band 67, No. 4, Apr. 1979 (IEEE, New York, U.S.A.), M. Ahmed et al., "Holography and its Application to Acoustic Imaging", Seiten 466-483, siehe Zusammenfassung.
Jung Yon
Moore David K.
Pritzl Werner
Wegener Bernd
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