Image analysis – Applications – Personnel identification
Reexamination Certificate
2000-07-07
2004-09-21
Boudreau, Leo (Department: 2621)
Image analysis
Applications
Personnel identification
C382S127000, C356S071000
Reexamination Certificate
active
06795570
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The invention is directed to a process for the electronic recording of an image of the surface of an object, which image can be displayed as a function G(x, y), wherein x and y are the coordinates of a respective image point of the image and G designates its gray value, wherein the object is recorded sequentially over different times t
i
, where t
i+1
>t
i
, from different perspectives as function G
i
in order to form the total image G from the individual images G
i
(x, y) such as when rolling a finger for recording a fingerprint, wherein portions are cut out of the individual images and joined together depending on the respective recorded view. The invention is further directed to an apparatus with a device for the electronic recording of an image of the surface of an object, which image can be displayed as image points by a function G(x, y), wherein x and y are the coordinates of the respective image point with an assigned gray value G, and with a device by which the object is imaged sequentially over different times t
i
where t
i+1
>t
i
, from different perspectives as function G
i
in order to form the total image G
i
from the individual images G
i
(x, y) such as when rolling a finger for the recording of a fingerprint, and an electronic image processing device whose circuit is designed to cut portions out of the individual images and join them together depending on the respective recorded view. The invention is further directed to a use of the process in an arrangement of the type described above.
b) Description of the Related Art
While image acquisition of flat images is presently carried out in a standard manner, there has been an increasing interest within technical circles in the imaging of three-dimensional bodies. Examples of applications in this respect include the recording of three-dimensional bodies in three spatial dimensions or two surface dimensions. These applications include tomography in the field of medicine and, in the consumer branch, automatic acquisition of human body dimensions for computer-assisted manufacture of tailor-cut clothing.
With techniques of these types, It is known to image a body from a plurality of views, wherein, in particular, an image recording device is guided around the body. In so doing, a plurality of recordings are made and the three-dimensional image of the body or the two-dimensional developed view of the surface is then reconstructed from these recordings in a computer.
The recording of the surface of a finger for acquiring fingerprints in criminology or for future applications for personal identification in security systems is more difficult.
The identification of persons has recently become a focus of interest in a computer technology. In the last year, for example, COMPAQ has offered computers which determine a numerical code from a fingerprint which can be used instead of a password for access to the Internet or for identification when making purchases on the Internet. For this purpose, the lines of the finger are determined by placing the finger on a sensor.
Compared with the examples mentioned above, the recording of fingerprints is particularly problematic. Because of the elasticity of the finger, the relevant lines of the finger can be displaced in the different recordings of the fingerprints, so that unique association is rendered dubious without special steps for classification.
For this reason, but also because of legal restrictions in most countries, it is attempted in criminology to record fingerprints in such a way that the technique of inking the finger to be recorded and rolling it on paper is simulated as far as possible. In so doing, a glass plate is usually used instead of paper, light being radiated onto the glass plate under total reflection conditions. When the finger is rolled, the lines of the finger interfere with total reflection due to their contact with the glass plate, so that the points of support are dark, resulting in a situation optically similar to that of a finger rolled on paper. The image occurring with different light intensities due to the total reflection is then electronically recorded and evaluated.
Although the process and apparatus which will be shown in more detail in the following can also be used for other applications such as those mentioned above by way of example, the following constructions are essentially directed to fingerprinting technique because the resulting set of problems in acquiring a curved surface can be shown especially clearly in this case.
During the rolling for electronic recording of individual images, recordings are made at determined times, so that the total image exists in steps as partial images of the rolling process, whereas a continuous imaging is carried out when recording on paper. The stepwise recording leads to the problem of deciding how to assemble the images. A simple assembly of the individual images is generally impossible because the finger deforms when rolled and even the structure of the lines of the finger changes when rolling. Similar problems also occur in tomography when the patient moves. Further, this is also true in the case of manufacturing tailored clothing by means of computers when the customer does not keep still. But this set of problems is particularly pronounced in the recording of fingerprints.
Known methods for reconstructing a total surface from individual images are known from U.S. Pat. No. 4,933,976, U.S. Pat. No. 5,230,025 and WO 97/41528. According to the teachings of these patents, a strip is removed the individual images and the total image is assembled from these strips. The cited patents differ from one another with respect to the different algorithms by which the strip boundary is determined in order, as far as possible, to join only parts of the individual images that correspond to the supporting surface of the finger. However, distorted or corrupted images can only be taken into account to a limited extent in the computing methods indicated in this case.
Inspection of the images recorded by these different methods show that many finger lines do not fit together perfectly or the image looks blurred with overlapping strips whose image content is averaged, which may be attributed to a slipping process of the finger at right angles to the rolling direction.
Conceivably, the matching of partial images could be improved by known mathematical algorithms for displacements, stretching and rotations, but the computing expenditure for mathematical processes of this type is so high that, given present processor speeds, the computing time for matching the large number of images recorded during the rolling process makes it impossible to record and evaluate the images within a time period comparable to that for rolling. In computing processes of this type, it would be more practical to roll a finger on paper in the standard way and to electronically process the flat fingerprint image made on the paper.
OBJECT AND SUMMARY OF THE INVENTION
For these reasons, it is necessary and an object of the invention to assemble sequentially acquired individual images electronically to form a total image in such a way that falsification due to unwanted movements of the imaged object can be taken into account better than is possible when strip-shaped partial images are fitted together, wherein the method used should also be capable of optimization with respect to shorter computing times compared to the image recording times.
Based on the process mentioned above, this object is met in that a curved intersection line is determined for defining the portions of every image aside from the first image by comparison with the image content of the previously recorded or assembled image G
i−1
, wherein the portion of the image G
i−1
is defined by this curved intersection line and the corresponding portion of the image G
i
is subsequently added to this intersection line to form the total image G (x, y), wherein this intersection line is determined by forming a simil
Eichhorn Torsten
Leszmann Ralph
Meister Andreas
Standau Joerg
Boudreau Leo
Dang Duy M.
Smiths Heimann Biometrics GmbH
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