Image analysis – Applications – Personnel identification
Reexamination Certificate
1999-04-23
2002-06-11
Johns, Andrew W. (Department: 2621)
Image analysis
Applications
Personnel identification
C356S071000
Reexamination Certificate
active
06404904
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process and a device for the identification of persons by optically reproducing hand and finger lines or prints without skin contact—denoted here as touchless—and a recognition algorithm for implementing the system.
2. The Prior Art
In the field of criminology, the patterns of the papillary ridges of the fingers have been employed for a long time by obtaining fingerprints on objects or on paper. These patterns have also been used by illiterate persons as their signature. More recently, these patterns have gained significance as an authorization control code for access to safes, safe-deposit rooms of banks, computers and other secured objects.
However, filing of a permanent color or hard-copy imprint is not practicable when it is desired to have an evaluation done by a computer rapidly. Also, these prior methods presuppose that the same applicator is in each case used frequently. Therefore, methods were developed first which make the picture of the imprint briefly visible on a glass surface through optical reproduction by exploiting impeded total or partial reflection on a refractive interface.
Patterns of the lines in the palm are also suitable for the identification of persons. Imprinting palm patterns on a glass surface is also feasible; however, this method failed to gain wide acceptance because the equipment would have to be substantially larger and more complicated to accommodate the palm. Therefore, the development of evaluation algorithms for this method has not yet reached an advanced stage.
A number of factors adversely affect an access control system based on a skin line imprint method, particularly one designed for use by a large number of persons unobserved and anonymously.
(1) In such systems, the measuring or contact pressure surface gets dirty to the point where the evaluation algorithm can no longer correctly function. Dirt, of course, could be removed by simply wiping it off, or if necessary with cleansing agents. However, the drawback is that the correct functioning of the system requires the cooperation and maintenance on the part of the participating people to keep the surface clean, which cannot always be expected, or alternatively, the user operating the system has to carry out the care and maintenance work, which is both cost- and labor-intensive.
(2) The contact surface of the sensor is a part of the path of the measuring rays that has to be always freely accessible, so that important components of the system may be damaged in the event of vandalism or sabotage.
(3) The contact pressure surface of the applicator is used by a great number of persons, which, for hygiene reasons, should be avoided, particularly in hospitals and medical and biological safety areas.
(4) The contact pressure surface of the applicator may transmit chemical or radioactive contamination.
(5) Methods requiring skin contact are less accepted than other methods for psychological reasons, for example, because of their association with a data file on “criminals”, fear of infection, or aversion to skin contact.
(6) Most known optical imprinting methods make a reproduction of the outermost surface of the skin by recording interference with the reflection on a surface of glass. This has a negative effect inasmuch as inhomogeneities of the skin disposed at deeper levels of the skin, as well as blood circulation patterns, which contain individual information as well, are not accessible in this way. This limits the clarity and definition of such methods.
(7) Many known methods of skin pattern detection are designed to determine the genuine surface structure of the skin (i.e., the relief of the skin). The drawback here is that plastic reproduction methods can easily reproduce the relief of the skin, which consequently creates possibilities for fraud.
(8) With all methods requiring skin contact, a slightly visible imprint, i.e., the classical imprint of a finger or hand line, remains on the surface of the apparatus. The drawback here is that this imprint can be made visible and can be misused with means employed for detecting and securing traces. For this reason, imprints made during skin contact methods must be removed, for example, by wiping them off in cases where high safety requirements need to be satisfied.
(9) The simple conventional method, which reproduces skin lines with a camera without contact with the object also has drawbacks. Since the skin is always slightly translucent under conventional illumination, and the light scattered diffused to a certain extent, and since the uppermost layer of the papillary ridges is reflected at the same time in a more or less shiny way, the camera, like the human eye, normally “sees” an undefined superpositioning of the images of the epidermis and hypodermis.
It is generally possible with illumination aimed at an angle, i.e., slanted, to increase the contrast of the papillary ridges and furrows of the skin. The drawback here is that this method does not work uniformly throughout the entire field of vision, but rather is dependent upon the direction of the line pattern relative to the illumination (shadow effects),. as well as upon the waviness of the surface of the object (gloss effects). Inclined illumination from all sides, or diffused illumination does in fact compensate for waviness optically, but deteriorates the contrast of the ridges because diffused reflection increases.
A relatively strong gloss and contrast effect is obtained with inclined illumination and inclined recording direction (according to the laws of reflection) particularly with large angles of incidence or recording. The drawback here is that when the object is set at an angle, or inclined, correction of distortion is required, for example according to SCHEIMPFLUG, which requires expensive equipment. The waviness of the skin also results in image distortions with this method.
SUMMARY OF THE INVENTION
The drawbacks of known methods as described above are reduced or eliminated according to the invention which relates to a process that works without skin contact.
By employing polarized light, the operating mode can be enhanced according to the invention. Polarizing light not only (a) substantially increases the contrast of the papillary ridges through preferred reproduction of the glossy or shiny structures, but also (b) filters out the shiny structures to make the papillary ridges visible so that the pattern of the hypodermis becomes visible. In particular, by using polarized light in the path of the illuminating rays and in the path of the reproducing light rays, it is possible to select in a defined way the pattern of the epidermis and the pattern of the hypodermis. The invention makes possible an accentuated representation of the shiny epidermis alone, an accentuated representation of the diffusely reflecting hypodermis alone, or a representation of both skin patterns in combination, for example one right after the other. The pattern of the hypodermis is predominantly supplied by the structures disposed at deeper levels, in particular by the structures of the adjacent layers of the skin that are already supplied with blood. In the case of linearly polarized light, the pattern of the epidermis is reproduced if the polarizing devices are set in parallel to the paths of the illuminating and reproducing rays, and the pattern of the hypodermis is reproduced when the polarizing devices are adjusted vertically.
In the case of circularly polarized light, the pattern of the epidermis is reproduced when the rotation of polarization in the paths of the illuminating and reproducing rays is adjusted in different senses, and the pattern of the hypodermis is reproduced when it is adjusted in the same sense. The direction of rotation (right or left rotation) is defined here as the direction of rotation of the E-vector, looking in the direction of propagation of the light.
The benefits offered by the invention can be described in detail as follows:
(1) The sensor system is protected against soiling or contamin
Einighammer Hans J.
Einighammer Jens
Azarian Seyed
Collard & Roe P.C.
Johns Andrew W.
TST-Touchless Sensor Technology AG
LandOfFree
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