U.S. patent application number 09/884838 was filed with the patent office on 2002-02-07 for method of and device for identification of fingermarks.
Invention is credited to Kroeninger, Mario, Lichtermann, Jan.
Application Number | 20020015515 09/884838 |
Document ID | / |
Family ID | 7646414 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020015515 |
Kind Code |
A1 |
Lichtermann, Jan ; et
al. |
February 7, 2002 |
Method of and device for identification of fingermarks
Abstract
Identification of a fingermark is performed by obtaining for a
fingermark a fingermark image, storing reference fingermarks in a
databank, comparing the obtained fingermark image with the
reference fingermarks for identification, before the identification
determining for each reference fingermark in comparison with the
obtained fingermark image a similarity degree, sorting the
reference fingermarks in the databank in accordance with the
similarity degree, and performing the identification of the
fingermark beginning with the reference fingermark which leads to
the greatest similarity degree.
Inventors: |
Lichtermann, Jan;
(Vaihingen-Ensingen, DE) ; Kroeninger, Mario;
(Buehl, DE) |
Correspondence
Address: |
STRIKER, STRIKER & STENBY
103 East Neck Road
Huntington
NY
11743
US
|
Family ID: |
7646414 |
Appl. No.: |
09/884838 |
Filed: |
June 19, 2001 |
Current U.S.
Class: |
382/124 ;
382/218 |
Current CPC
Class: |
G06V 40/1365
20220101 |
Class at
Publication: |
382/124 ;
382/218 |
International
Class: |
G06K 009/00; G06K
009/68 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 21, 2000 |
DE |
100 30 404.4-53 |
Claims
What is claimed as new and desired to be protected by Letters
Patent is set forth in the appended claims.
1. A method of identification of a fingermark, comprising obtaining
for a fingermark a fingermark image; storing reference fingermarks
in a databank; comparing the obtained fingermark image with the
reference fingermarks for identification; before the identification
determining for each reference fingermark in comparison with the
obtained fingermark image a similarity degree; sorting the
reference fingermarks in the databank in accordance with the
similarity degree; and performing the identification of the
fingermark beginning with the reference fingermark which leads to a
greatest similarity degree.
2. A method as defined in claim 1; and further comprising
performing the identification in accordance with a details
comparison.
3. A method as defined in claim 1; and further comprising
performing the identification in accordance with a correlation of
the fingermark with the corresponding reference fingermark.
4. A method as defined in claim 1; and further comprising
determining the corresponding similarity degree by a comparison of
properties of a corresponding area around a reference point of the
fingermark with each property of the corresponding area of the
reference fingermark.
5. A method as defined in claim 4; and further comprising using
core and delta points as reference points.
6. A method as defined in claim 5; and further comprising placing
square areas around the reference point of the fingermark;
multiplying the area with window function; transforming the area by
means of a first integral transform in a space frequency region;
determining features in the areas of the reference point;
evaluating for the features the space frequencies in accordance
with amount and direction; and determining by the features of the
fingermark and the reference fingermark correspondingly the
similarity degree for the corresponding reference fingermark.
7. A method as defined in claim 6; and further comprising laying
the square areas in different sizes.
8. A method as defined in claim 6; and further comprising breaking
a power density spectrum of the areas of the reference points in
sectors and rings; summing for the sectors and the ring the powers
of the corresponding containing space frequencies so that for the
sectors a degree for the orientation is provided and for the rings
a degree for the amount; forming thereby a ring vector and a sector
vector; forming the ring vector and the sector vector as a feature
vector; and comparing with a feature vector of the reference finger
marks to determine the similarity degree.
10. A method as defined in claim 9; and further comprising joining
the comparison of the ring vector and the sector vectors before and
after a second integral transform to the similarity degree for the
corresponding reference fingermark.
11. A method as defined in claim 10; and further comprising
performing the comparison by a method selected from the group
consisting of a difference square method and a correlation
method.
12. A method as defined in claim 1; and further comprising
selecting regions on the fingermark so that the regions have only
papillar lines.
13. A device for identification of a fingermark, comprising a
processor; a databank; a work storage; an indicator and a
fingermark sensor for determination of a fingermark image, said
processor being formed so that said processor compares a fingermark
image with reference marks stored in said databank to determine a
similarity degree for each reference fingermark, said processor
sorting the reference fingermarks in said databank in accordance
with the similarity degree, said processor performing
identification of the fingermark starting with the reference
fingermark with a greatest similarity degree, said processor
exhibiting a result of the identification with said indicator.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method for identification
of a fingermark, and a device for identification of a
fingermark.
[0002] The patent document WO99/05637 discloses a method and a
device for placing an unknown finger mark in a category. The
analysis is performed in a spatial frequency region. The image of
the fingermark is subdivided in the spatial frequency region into
regions. These regions are sectors, to each of which a value is
assigned. This value is derived from the energy of the spatial
frequencies which are to be found in these sectors. The stored
values are associated with the category, but not with a fingermark.
Therefore a comparator is utilized, which preferably provides a
correlation. The values are transformed by a one-dimensional
Fourier transform, in order to then perform finally the correlation
by means of this transformed value. If a coincidence is determined,
then the unknown fingermark is classified in a corresponding
category.
SUMMARY OF THE INVENTION
[0003] Accordingly, it is an object of the present invention to
provide a new method of and device for identification of a
fingermark.
[0004] In keeping with these objects and with others which will
become apparent hereinafter, one feature of present invention
resides, briefly stated, in a method of identification of a
fingermark, which comprises the steps of obtaining for a fingermark
a fingermark image; storing reference fingermarks in a databank;
comparing the obtained fingermark image with the reference
fingermarks for identification; before the identification
determining for each reference fingermark in comparison with the
obtained fingermark image a similarity degree; sorting the
reference fingermarks in the databank in accordance with the
similarity degree; and performing the identification of the
fingermark beginning with the reference fingermark which leads to
the greatest similarity degree.
[0005] In accordance with another feature of present invention, a
device for identification of a fingermark is provided, which has a
processor; a databank; a work storage; an indicator and a
fingermark sensor for determination of a fingermark image, said
processor being formed so that said processor compares a fingermark
image with reference marks stored in said databank to determine a
similarity degree for each reference fingermark, said processor
sorting the reference fingermarks in said databank in accordance
with the similarity degree, said processor performing
identification of the fingermark starting with the reference
fingermark with a greatest similarity degree, said processor
exhibiting a result of the identification with said indicator.
[0006] When the method is performed and the device is designed in
accordance with the present invention, they have the advantage that
an identification of a fingermark is possible. It is also
advantageous that the time for the identification because of the
sorting of the stored reference fingermarks in a data bank is
lowered. Thereby it is possible, with a same counting time, to
accept higher user numbers. The inventive method also is reliable
and robust against errors. Thereby the use in the identification
systems of this method is possible.
[0007] Moreover, the inventive method has the advantage that it is
performed with a categorization, so that error connected with the
categorization can not occur.
[0008] In accordance with a further advantageous feature of the
present invention, alternatively to the details comparison, a
predetermined number of details is used for identification. When
this predetermined number is reached, the fingermark is considered
as identified. For example, when twelve or eighteen details in the
fingermark and in the reference fingermark coincide, an
identification is obtained. For this purpose, preferably a
threshold value can be used.
[0009] Furthermore, there is an advantage, that alternatively to
the details, a correlation method for identification of the
fingermark is utilized. For this purpose for example a correlation
coefficient is calculated, which is compared with a predetermined
threshold value. If the correlation coefficient is located above
the threshold value, then the fingermark is considered as
identified. Furthermore, there is an advantage that the fingermarks
and the reference fingermarks are characterized by reference points
(singularity), for example of core and delta points. Thereby an
accurate determination of the position of the fingermark is
possible: the fingermark can be placed in different positions on
the fingermark sensor to generate the fingermark image, and the
fingermark is determined in accordance with the reference points
and/or the area around the reference point with respect to its
position, and a similarity is determined in comparison with a
stored fingermark.
[0010] In accordance with still a further feature of the present
invention, from the fingermark, square areas around a fixedly
defined point, for example a reference point (singularity) are
taken and, for the analysis in the transformation performed in the
frequency region, is multiplied with a rotation-symmetrical window
function, for example a two-dimensional Gauss bell. Thereby in
particular the corners are taken away, so that during turning
always the same informations are provided in the area. Furthermore,
by the comparison of the stored reference points, it is possible
preferably to identify pronounced reference points in a fingermark.
The area on the other hand is characterized in that, for the
spatial frequency an amount and a direction are determined, in
particular with the use of the power density spectrum. Therefore by
means of this feature, a similarity can be determined from the
comparison of the fingermark and the corresponding reference
fingermark. The areas are compared, which are located at
corresponding locations on the fingermark and the corresponding
reference fingermark.
[0011] In accordance with a further feature of the present
invention, it is advantageous that with the use of different values
for the square areas it is possible to use only such areas, in
which all papillar lines are to be found. This is important
especially in view on the edge regions, where a square of
determined value can embrace also the region outside of the
fingermark and thereby finally falsify the identification.
[0012] In accordance with still a further advantageous feature of
present invention, a region to be analyzed after the transformation
is subdivided into the frequency region on the fingermark in
sectors and rings. The sectors provide an angle determination and
the power determination inside the sectors and the rings provides
an expression over the frequency available in the region to be
analyzed in accordance with direction and amount. The power
distribution over the ring or sectors is stored in a ring vector or
sector vector, which together serve as a feature vector. This
feature vector is used for determination of the similarity value,
in which the feature vector is compared with the feature vector of
the corresponding reference fingermark. By interpolation,
additional components fort he feature vector can be determined.
[0013] In accordance with a further advantageous feature of present
invention, by a one-dimensional Fourier transform as an integral
transform of the sector vector, a comparison of turned fingermarks
is facilitated. Furthermore, it is advantageous when the similarity
value is determined by a difference square method or a correlation
method. It is further advantageous when the area sizes on the
fingermark around the corresponding utilized reference point are
selected so that, only papillar lines are located in the regions as
objects. Thereby a well-defined analysis and a comparison with the
reference fingermarks is possible.
[0014] Finally, in accordance with a further advantageous feature
of the present invention, the reference points in the fingermark
image are determined by a comparison of orientation methods with
stored orientation methods. This makes possible a very accurate
determination of the reference points and thereby increases the
accuracies of the inventive method.
[0015] The novel features which are considered as characteristic
for the present invention are set forth in particular in the
appended claims. The invention itself, however, both as to its
construction and its method of operation, together with additional
objects and advantages thereof, will be best understood from the
following description of specific embodiments when read in
connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a view showing a block diagram of a device for
identification of fingermarks in accordance with the present
invention;
[0017] FIG. 2 is a flow diagram of a method for identification of
fingermarks in accordance with the present invention; and
[0018] FIG. 3 is a view showing the subdivision of the region of
the fingermark into rings and sectors.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] Identification systems for users are utilized in various
areas of life for safety reasons. In order to obtain access to
automobiles, buildings and special spaces, a definite
identification of the user, which only the user possesses must be
guaranteed. Since only the user must have this identification
feature, a body feature can be used which a user naturally always
has with him. A feature which for each person is different is then
fingermark. If a fingermark must be identified for example for the
banking business, then the arrangement for identification of the
fingermarks must have a databank with stored reference fingermarks,
and the fingermark and the reference fingermarks must be
systematically compared to determine a coincidence or absence of a
coincidence therebetween. The method must operate fast and accurate
since it is used for safety-relevant systems.
[0020] In accordance with the present invention, the reference
fingermarks are sorted in the databank with the inventive
arrangement in accordance with a similarity degree. This similarity
degree is formed by a simple comparison of the fingermark to be
identified with all reference fingermarks. For each reference
fingermark a similarity degree is provided. The reference
fingermarks are sorted in accordance with the value of the
similarity degree, so that the fingermark with the greater
similarity degree or in another words with the greater similarity
with the fingermark to be identified is first compared with the
fingermark to obtain an identification. This identification is then
carried out with a known method for identification, or in other
words a details comparison or a correlation technique. The
similarity degree is available by a comparison of properties of the
area around a reference point with the properties of the stored
fingermarks. A comparison of the same space of the fingermarks is
performed. Corresponding areas of the stored fingermarks are
utilized. This leads to a higher accuracy of the method.
[0021] FIG. 1 shows a block diagram of the inventive device for
identification of fingermark. A fingermark sensor 1 is connected
through a data outlet with a processor 2. A databank 3 is connected
to a first data inlet/outlet of the processor 2. A work storage 4
is connected to a second data inlet/outlet of the processor 2. The
signal processing unit 5 is connected to a data outlet of the
processor 2. An indicator 6 is connected to a first data outlet of
the signal processing unit 5. A loudspeaker 7 is connected to a
second data outlet of the signal processing unit 5.
[0022] An optical system can be utilized as a fingermark sensor 1.
The effect of total reflection is utilized to transform the
three-dimensional data of the finger surface into a two-dimensional
data quantity. A core piece is a 90.degree. prism with a hypotenuse
on which the fingertip is applied, while in one cathetus of the
prism the parallel light is coupled and the brightness distribution
of the other cathetus is digitalized via an CCD array and a frame
digger. This is a process which is generally known as scanning. At
the location, at which the raised papillar lines contact the prism
surface, light is uncoupled by the local change of the refraction
indices light. The arrays papillar lines are represented in the
digital image as dark lines. Valleys to the contrary are
represented as bright lines, since they do not disturb the total
reflection. Alternatively it is possible to use a capacitor sensor.
These capacitor sensors, when compared with the optical systems
have the advantage of the smaller size and lower price. A
capacitive sensor is composed in principle of a plurality of small
capacitive individual elements which are integrated in standard
CMOS technology on a chip.
[0023] Digital data are presented at the outlet of the fingermark
sensor 1 and then are further processed by the processor 2. The
databank 3 is here formed as a semiconductor storage. It is however
also possible to use a magnetic storage, or in other words a hard
disk. The work storage 4 is used for intermediate storing for the
calculations. The signal processing unit 5 drives the indicator 6
or the loudspeaker 7, depending on the data which are transmitted
from the processor 2 to the signal processing unit 5. If an
identification of the fingermark is obtained by the processor 2,
then the processor 2 of the signal processing unit 5 provides such
an information which is reproduced on the indicator 6 or the
loudspeaker 7. Alternatively it is possible to dispense with either
the indicator 6, or the loudspeaker 7. The loudspeaker 7 has an
audio amplifier and a digital/analog converter to convert the
digital signals coming from the signal processing unit 5 into
analog audio signals. In addition to or instead of the indicator
which identifies a fingermark, it is also possible to couple an
actuator with the inventive device. Such an actuator can be for
example a door opener.
[0024] FIG. 2 illustrates the inventive method for identification
of a fingermark as a flow diagram.
[0025] The record of the fingermark is produced in the method step
8 by the fingermark sensor 1. The fingermark image can be produced
as a whole or in parts. This fingermark image is then transmitted
to the processor 2. In the method step 9 the processor 2 breaks the
fingermark image into regions, which are then used for the
orientation estimate. The orientation estimate is important for the
determination of a similarity degree. During this region selection,
features are provided in order to select only such regions which
have all papillar lines. This is possible by an evaluation in the
frequency region, or more correctly in the power density spectrum.
The property is utilized so that areas which embrace all papillar
lines in a predetermined frequency region which can be determined
as the typical papillar line distance have a higher spectral power
density than such which have not only papillar lines as image
objects. Therefore a threshold value comparison for the power
density spectrum is performed. The threshold value is set so that
when the measured light density is located over the threshold value
it can be concluded that the searched image regions have all
papillar lines.
[0026] In method step 10 a two-dimensional Fourier transform of the
individual regions is performed. A Fourier transform is an integral
transform. Alternatively, other types of integral transforms can be
utilized. In particular, wavelets are suitable for this purpose.
With wavelets, a transform with a special adjusted transform is
performed.
[0027] In method step 11 then the reference points are searched in
the individual regions in a space region. The regions are assembled
to image regions to identify the reference points in the image
regions in accordance with a comparison of orientation courses.
This is performed by the comparison of orientation courses in the
fingermark image and the stored orientation courses which identify
the reference points. First the fingermark image is filtered in the
frequency region locally with a band pass for producing a useful
frequency region. Disturbances are therefore eliminated. The useful
frequency region is then locally ratedly squared to compute a
spectral power density for the corresponding region. The
frequencies in the useful frequency region are weighted in the
corresponding region with the associated spectral power density, in
order to calculate with this weighted frequencies a regression
straight line for the corresponding region. Thereby the orientation
of the papillar lines is determined in the corresponding region. In
the image regions which are assembled of several regions, then a
search is performed in accordance with the reference points. The
regions, as mentioned above, can be assembled to areas, and by a
comparison with the stored reference orientation courses of the
image regions, a corresponding reference point can be identified
for an image region. Core and delta points are searched as
reference points (singularities) to be identified. The reference
points on a fingermark define the fingermark itself and with
respect to their position, and they supply a reference points for a
coordinate system.
[0028] In method step 12, square areas are placed around the
reference point, for example 32.times.32 pixel. These square areas
are provided in several sizes, since in particular at the edge
region of a fingermark image a square around a reference point of a
predetermined size can detect an area which does not contain
papillar lines. For this purpose around each reference point a
square with different predetermined sizes is provided. The square
is then multiplied with a window function, here a two-dimensional
Gaussing function, so that a circular cutout is produced. A circle
is insensitive in particular to turnings.
[0029] In method step 13 the areas multiplied with the window
function are subdivided into sectors and rings. Before the areas
are two-dimensionally Fourier-transformed and then a squaring is
performed to determine the power density spectrum. Since a Fourier
transform is used as an integral transform, a real value signal in
the frequency region has two signals which are symmetrical to an
origin. Thereby a half of the power density spectrum can be used
fort he subdivision into rings and the other half of the power
density spectrum can be used for the division in sectors.
[0030] FIG. 3 shows the division of the power density spectrum of a
region with rings and sectors. Sectors 24 are provided in the upper
half of the square, while the rings 25 are formed in the lower
half. The sectors 24 are utilized to obtain an information or the
orientations which take part in one region, while the rings are
utilized to obtain an information over the frequency regions which
take part in one region. The sectors 24 are circularly limited
because of the window function. Since a two-dimensional Fourier
transform is utilized, the frequencies have an amount and an angle
which are provided as vectors.
[0031] In method step 14 the feature determination for the
individual sectors 24 and the circular rings 25 is provided. For
this purpose the power of the individual frequencies in the sectors
or rings is summed for the corresponding sectors and rings, so that
for the sectors the sum of the power of the individual frequencies
provides a degree for the corresponding orientation, while for the
rings the sum of the frequencies provides a degree for the
corresponding amount. This gives corresponding components a
sector-or ring vector. Alternatively, by means of an interpolation
the number of the rings and sectors can be subsequently increased.
This can be required in particular for an adaptation of the data
sets. The ring vector and the sector vector together form the basic
shape of the papillar line course in a corresponding area.
[0032] The basic idea is that two areas which contain substantially
the same image information must also have substantially coinciding
portions with the orientation and frequency portions occurring in
the cutout, or in other words the sector and the ring components.
For the ring components this is true independently from a turning
of the both finger marks, since by integration over all
contributing angles, these ring components are calculated.
[0033] The sector vectors are first not rotation-independent.
Because of the rotation property of the Fourier transform, during a
rotation of the image cutout a cyclical displacement of the sector
components is performed, since the spectrum of a turned region also
turns. Since sector vector deals with a cyclical or periodic
feature vector, with which the first and the last value transit
into one another, this feature vector before the later comparison
is transformed into the one-dimensional frequency region. Thereby a
feature vector is obtained, which is independent from the turning
angle. Also the ring vector is Fourier transformed in accordance
with the inventive method. This is performed in the method step 15.
Instead of the Fourier transform as the integral transform, also
other types of integral transforms can be used, in particular the
wavelets.
[0034] In method step 16 a comparison of the Fourier-transformed
ring vectors and the Fourier-transformed sector vectors of the
fingermark to be identified and the corresponding reference
fingermark is performed. The comparison takes place for vectors
which are produced for a corresponding space on the fingermark and
the corresponding reference fingermark. In addition, also a
comparison of the non-transformed ring vectors or sector vectors is
performed. The comparisons take place at the same spaces on the
fingermark and on the corresponding reference fingermark. Thereby
four comparisons are performed. In the method steps 17, from these
four comparisons or in other words the four similarity degrees, a
similarity degree is determined by binding (linking). This is
performed either by a weighted addition or by a multiplication.
[0035] In the method step 18, with the similarity degrees for the
corresponding reference fingermark, a sorting of the data bank 3 in
accordance with the magnitude of the similarity degree is performed
by the processor 2. The reference fingermark with the greatest
similarity degree is located at the first place.
[0036] In the method step 19, starting with the reference
fingermark which has the greatest similarity degree, the
identification is performed. It has performed by means of a detail
comparison. A predetermined number of details is taken as a
presumption for an identification. For example, twelve details of
the fingermark and the reference fingermark must coincide, so that
one can speak about an identification. Details means local features
which are identified by individual papillar lines. Papillar lines
are for example the skin grooves on the inner hand surface.
[0037] Alternatively it is possible to calculate a correlation
coefficient by correlation of the fingermark with the reference
fingermark, and compare it with a predetermined threshold value. If
the correlation coefficient is located above the threshold value,
then an identification is indicated. If it is located below, there
is no identification. In method step 20 it is verified whether an
identification is provided. If this is the case, in method step 21
by means of the indicator 6 or the loudspeaker 7 it is indicated
that the fingermark is identified and in some cases a data set
bound with the reference fingermark is brought for identification.
This can involve for example a person, such as a name or an image
of the person. Alternatively, also the activation of an actuator is
also possible, for example for opening a door.
[0038] If in method step 20 it is determined that no identification
takes place, then in method step 22 it is evaluated whether the
data bank was completely searched. If this is not the case, then in
method step 19 the process continues with the next reference
fingermark in the data bank. If in method step 22 it is however
determined that the data bank is completely searched, then in
method step 23 it is indicated that the presented fingermark is not
identifiable.
[0039] It will be understood that each of the elements described
above, or two or more together, may also find a useful application
in other types of methods and constructions differing from the
types described above.
[0040] While the invention has been illustrated and described as
embodied in a method of and device for identification of
fingermarks, it is not intended to be limited to the details shown,
since various modifications and structural changes may be made
without departing in any way from the spirit of the present
invention.
[0041] Without further analysis, the foregoing will so fully reveal
the gist of the present invention that others can, by applying
current knowledge, readily adapt it for various applications
without omitting features that, from the standpoint of prior art,
fairly constitute essential characteristics of the generic or
specific aspects of this invention.
* * * * *