Image analysis – Applications – Personnel identification
Reexamination Certificate
1999-12-16
2003-12-02
Wu, Jingge (Department: 2623)
Image analysis
Applications
Personnel identification
C382S115000, C382S124000, C356S071000, C340S005830
Reexamination Certificate
active
06658140
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The invention is directed to a method for obtaining image information, for example, about the surface configuration or surface structure of the palm or inside surface of a hand, the edge of a hand, the extended four fingers or an extended thumb, wherein the object to be recorded is placed on a scanning surface, an image of the surface structure is recorded with an illumination beam path directed onto the scanning surface and reflected by the scanning surface, and this image is subsequently projected onto the reception surface of an optoelectronic image converter. The invention is further directed to an arrangement for carrying out the method.
b) Description of the Related Art
Capture of impressions for the traditional formats consisting of rolled individual fingers, flat, plain (not rolled) four extended fingers of the hand which are to be captured simultaneously, and flat, plain (not rolled) extended thumb is known in the art. The size of the scanning surface is typically about 40 mm×40 mm for rolled individual fingers and about 75 mm×58 mm for flat simultaneous impressions of the four extended fingers. The optoelectronic scanning devices are adapted to these formats.
The capture of impressions of the kind mentioned above or of the pattern of papillary lines is based on the fundamental optical principle of frustrated total reflection. In known optoelectronic processes and arrangements, this basic principle is applied essentially by adapting to the specific conditions of the available image converters which usually take the form of CCD cameras. At the same time, this also results in the need for adapting to the limited quantity of light-sensitive sensors available in the image converter in the horizontal and vertical directions with respect to optical requirements.
DE 34 21 220 C2 describes a device for the capture, examination and identification of fingerprints in which a distortion-free optical imaging of the fingerprint is carried out on the light-receiving surface of a TV camera. The aspect ratio of the finger scanning surface is transmitted unchanged to the sensor of the TV camera by means of the special optical arrangement wherein deflecting prisms for anamorphotic magnification of the fingerprint and for compensation of astigmatism are provided between the reflecting prism and the image-side end part of the device.
It is disadvantageous in this arrangement that the need to provide a distortion-free optical arrangement can result in prisms with very small angles which are technologically difficult to produce and whose use in the device, moreover, leads to problems with respect to adjustment and image quality because of very strict permissible tolerances.
U.S. Pat. No. 5,650,842 describes an optical arrangement which is directed exclusively to the recording of four fingers simultaneously. The rectangular format of the finger scanning surface is imaged on a CCD camera with an extreme aspect ratio of about 1.6:1 by a special optical arrangement in such a way that the image matches the aspect ratio of the sensor surface by approximately 1.33:1. This strong optical distortion in the horizontal direction by a factor of 0.831 is compensated subsequently during readout of the analog image signals prepared by the CCD camera with oversampling by a factor of 1.203.
This procedure is disadvantageous in that, in order to obtain a clean signal shape, the analog signal must be sharply defined in its bandwidth so that no interference occurs in the oversampled digital image signal. This has a negative effect on optical resolution in the horizontal direction. Also, in the above-cited reference the imaging beam path is guided away from the finger scanning surface in the direction of the vertical axis of the image. However, the device housing must therefore be disadvantageously increased in size toward the front, i.e., toward the user, and a vertical closing surface must be provided, which greatly encumbers accessibility particularly when recording the flat extended thumb, or even renders capture impossible in the case of persons with limited articulation of the fingers.
An essential requirement in the capture of fingerprints, above all in law enforcement entities, is to generate images of the highest optical quality so as to provide the foundation for the input and use of the images in automatic fingerprint and hand-impression identification systems and to ensure a high rate of hits in the comparison with images which are already stored.
For this reason, spatial resolution may not fall below a minimum and geometric distortion may not exceed a maximum. A high spatial resolution is important for clear, sharp visibility of even fine structures in the papillary lines; reduced distortion offers the assurance of definite determination of the characteristic features, the minutiae, as they are called. Further, a good image contrast is a further prerequisite.
There is also an increasing desire on the part of users of identification systems of the type mentioned above to be able to capture images of the inside surface, the edge of the hand, the extended thumb, the extended four fingers, etc. with only one device and also with one and the same scanning surface present in this device, so that it is no longer necessary to have available a plurality of different application-specific devices in order to carry out all of the tasks performed by entities concerned with identification.
The solutions available in the prior art up to this point are not suitable for comprehensively meeting the above-mentioned requirements.
OBJECT AND SUMMARY OF THE INVENTION
Proceeding from the prior art, it is the primary object of the invention to further develop a method of the kind described above in such a way that the flat or plane image of the inside surface of a hand and/or the edge of a hand and/or the extended four fingers and/or extended thumb is generated by one and the same scanning surface with high image quality and in a comfortable manner for the person in question.
According to the invention, this object is met in that the image of the surface structure is recorded with an aspect ratio B
A
:H
A
<1, wherein the fingers of the hand placed on the scanning surface are oriented parallel to height H
A
, the aspect ratio of the image is changed during the optical transmission from the scanning surface to the optoelectronic image converter, wherein the height is compressed in such a way and/or the width is expanded in such a way that an image which is optically distorted to the aspect ratio of B
E
:H
E
>1 reaches the reception surface, the optically distorted image is then converted into electronic image information, wherein exactly one analog or digital value is obtained for every output signal of an individual sensor, and the electronic image information then undergoes a calculated or computational change in the aspect ratio, wherein the height is computationally expanded and/or the width is computationally compressed until the original aspect ratio B
A
:H
A
<1 has been restored.
In this way, it is possible to utilize a scanning prism whose scanning surface is sufficiently large to capture the entire inside surface of the hand. By means of preferably anamorphotic optics arranged after the scanning surface, the aspect ratio of the optical image recorded by this scanning surface is distorted in a defined manner by expanding and/or compressing and is directed via an imaging objective to the reception surface (for example, of a CCD camera), where the optical image information is converted to analog electronic image information, wherein, according to the invention, the aspect ratio is not changed.
Subsequently, the analog electronic image information is digitized. In contrast to the prior art, this is done in such a way that exactly one digital value is formed for every unit of analog image information read out of an individual light-sensitive CCD sensor. Accordingly, an image point-synchronized digitization is carried out while maintaining the di
Hillmann Juergen
Richter Uwe
Heimann Biometric Systems GmbH
Hesseltine Ryan J.
Reed Smith LLP
Wu Jingge
LandOfFree
Method and arrangement for obtaining image information... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and arrangement for obtaining image information..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and arrangement for obtaining image information... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3127573