A Novel Approach to Fingerprint Identification Using Gabor Filter-Bank

ACEEE Int. J. on Network Security , Vol. 02, No. 03, July 2011

A Novel Approach to Fingerprint Identification Using
Gabor Filter-Bank
Ms.Prajakta M. Mudegaonkar 1 , Prof.Ramesh P. Adgaonkar 2
1 Student of Master of Engineering in Computer Science, GSM’s Marathwada Institute of Technology,
,
Beed By-Pass Road, Aurangabad, Maharashtra, India.
Email: pmm997@gmail.com
2 Department of Computer Science and Engineering, GSM’s Marathwada Institute of Technology,
,
Beed By-Pass Road, Aurangabad, Maharashtra, India.
Email: rp_adgaonkar@rediffmail.com

Abstract ”Fingerprint Identification is a widely used Biometric Although the fingerprints possess the discriminatory
Identification mechanism. Up till now different techniques information, designing a reliable automatic fingerprint
have been proposed for having satisfactory Fingerprint matching algorithm is very challenging. As fingerprint sensors
Identification. The widely used minutiae-based representation are becoming smaller and cheaper, automatic identification
did not utilize a significant component of the rich based on fingerprints is becoming an attractive alternative/
discriminatory information available in the fingerprints. Local
complement to the traditional methods of identification. The
ridge structures could not be completely characterized by
minutiae. The proposed filter-based algorithm uses a bank of
critical factor in the widespread use of fingerprints is in
Gabor filters to capture both local and global details in a satisfying the performance (e.g., matching speed and
fingerprint as a compact fixed length Finger Code. The accuracy) requirements of the emerging civilian identification
Fingerprint Identification is based on the Euclidean distance applications [2]. Some of these applications (e.g., fingerprint-
between the two corresponding Finger Codes and hence is based smartcards) will also benefit from a compact
extremely fast and accurate than the minutiae based one. representation of a fingerprint.
Accuracy of the system is 98.22%.
II. FINGERPRINT IDENTIFICATION
Index Terms ”Core Point, Euclidean Distance, Fingerprints,
Feature Vector, Finger Code, Gabor Filter-bank. Fingerprint matching techniques can be broadly
classified as minutiae based and correlation based [5].
I. INTRODUCTION Minutiae based technique first located the minutiae points in
a given fingerprint image and matched their relative
Fingerprint-based identification is one of the most placements in a stored template . The performance of
important biometric technologies which has drawn a this technique relied on the accurate detection of
substantial amount of attention recently. Humans have used minutiae points and the use of sophisticated matching
fingerprints for personal identification for centuries and the techniques to compare two minutiae fields which undergo
validity of fingerprint identification has been well established. non-rigid transformations. Correlation based techniques
Among all the biometrics fingerprint- based identification is compared the global pattern of ridges and valleys to see if
one of the most mature and proven technique. Fingerprints the ridges in the two fingerprints align. The global approach
are believed to be unique across individuals and across to fingerprint representation was typically used for indexing
fingers of same individual [1],[2]. These observations have and did not offer reliable fingerprint discrimination.
led to the increased use of automatic fingerprint-based
identification in both civilian and law-enforcement
applications. A fingerprint is the pattern of ridges and valleys
on the surface of a fingertip. When fingerprint image is
analyzed at global level, the fingerprint pattern exhibits one
or more regions where ridge lines assume distinctive shapes.
These shapes are characterized by high curvature,
terminations, bifurcations, cross-over etc. These regions are
called singular regions or singularities [5]. These singularities
may be classified into three topologies; loop, delta and whorl.
At local level, there are other important features known as
minutiae can be found in the fingerprint patterns. Minutiae
mean small details and this refers to the various ways that
the ridges can be discontinuous. A ridge can suddenly come
to an end which is called termination or it can divide into two Fig.1 Ridge ending, core point and ridge bifurcation
ridges which is called bifurcations as shown in Fig. 1 [5].
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DOI: 01.IJNS.02.03.159


The ridge structure in a fingerprint can be viewed as an fingerprints which are translation and rotation invariant. In
oriented texture patterns having a dominant spatial frequency the proposed scheme, translation was taken care of by core
and orientation in a local neighborhood. The frequency is point during the feature extraction stage and the image
due to inter ridge-spacing present in a fingerprint and the rotation was handled by a cyclic rotation of the feature values
orientation is due to the flow pattern exhibited by ridges. By in the feature vector. The features were cyclically rotated to
capturing the frequency and orientation of ridges in local generate feature vectors corresponding to different
regions in the fingerprint, a distinct representation of the orientations to perform the matching.
fingerprint is possible. In this paper I mainly focused on
A. Core Point Detection
Gabor Filter-bank based Fingerprint Identification..Since
Gabor Filters are characterized by spatial frequencies and For having satisfactory Fingerprint Identification, finding
orientation capabilities, they are best suited for fingerprint exact reference point or core point was an important task.
identification [3]. Single Gabor Filter function was not Since core point was nothing but a high curvature region in
sufficient for capturing whole global and local fingerprint the fingerprint, it’s totally dependent on the orientation of
information therefore bank of Gabor filters was prepared with ridges. Therefore orientation field of the fingerprint was
8 Gabor Filters. Detailed filter-bank based feature extraction estimated. The typical orientation field of a fingerprint is
procedure is discussed in upcoming sections. shown in Fig. 3 as in [8].Steps for orientation field estimation
are discussed below. Let è be defined as the orientation field
III. GABOR FILTER-BANK BASED FEATURE of a finger print image. è(i,j) represents the local ridge
EXTRACTION orientation at pixel (i,j). Local ridge orientation, however, was
usually specified for a block rather than that of every pixel.
In the proposed system initially core point in fingerprint Thus, an image was divided in to a set of non-overlapping
image was detected [2],[5]. The core point corresponds to blocks of size w×w. Each bock held a single orientation. In
center of loop type singularity. Some fingerprints did not connection with the work outlined in this paper, the smoothed
contain loop or whorl singularities, therefore it was difficult orientation field based on least mean square algorithm is
to define core. In that kind of images, core is normally summarized as follows as in [2],[8] :
associated with the maximum ridge line curvature. Detecting 1. The input image I was divided into non-overlapping blocks
a core point was not a trivial task. For finding core point, with size w×w.
initially orientation field was estimated. [7],[8],[9]. For that 2. Gradients äx(i,j) and äy(i,j) were calculated, at each pixel
one algorithm is discussed here. Fig. 2 shows an optimal core (i,j) which was the center of the block.
point in an fingerprint image, as in [5].After getting a core 3. Local orientation was estimated using the following
point, circular region around the core point was tessellated equations :
into 80 sectors. The pixel intensities in each sector were The gradient operator can be chosen according to the
normalized to a constant mean and variance. The circular computational complexity. Generally sobel operator is used.
region was filtered using a bank of eight Gabor filters to
produce a set of eight filtered images. The average absolute
deviation with in a sector quantifies the underlying ridge
structure and was used as a feature. A feature vector (640
bytes in length) was collection of all the features, computed
from all the 80 sectors, in every filtered image. The feature
vector captured the local information and the ordered Subsequently,
enumeration of the tessellation captured the invariant global
relationships among the local patterns. The matching stage
computed the Euclidean distance between the two
corresponding feature vectors. It is desirable to obtain
representations for

Fig. 3 Fingerprint Orientation Map (a) Orientation Field mapped
over Fingerprint (b) Orientation Field Map

local ridge orientation at the block with the centered at pixel
Fig. 2 Optimal Core Point Lcation (i,j).

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© 2011 ACEEE
DOI: 01.IJNS.02.03.159


4. The discontinuity of ridge and valley due to noise could concentric bands around core point. Each band is 20 pixels
be soften by applying a low pass filter. However, to apply a wide and segmented into sixteen two sectors. Thus there
low pass filter the orientation image must be converted to a were total 16 x 5 = 80 sectors and the region of interest was a
continuous vector field. The continuous vector field, which circle of radius 100 pixels, centered at the core point. The
its x and y components are defined as Öx and Öy respectively. tessellated region of interest is shown in Fig. 5.

IV. FILTERING
Before filtering the fingerprint image, the region of
interest was normalized in each sector separately to a
With the resulted vector field, the two dimensional low- pass constant mean and variance. Normalization was performed
filter G with unit integral was applied .The specified size of to remove the effects of sensor noise and gray level
the filter was ,as a result, deformation due to finger pressure differences as given in
[3],[5]. I(x,y) denoted the gray value at pixel (x,y), and ,the
estimated mean and variance of sector , respectively,and
, the normalized gray-level value at pixel (x,y). For all
the pixels in sector , the normalized image was defined as:

5. The smoothed orientation field local ridge orientation at
(i,j) was then computed as follows:

Now after finding out the smoothed orientation field, core Where and were the desired mean and variance values,
point was found out. For locating this reference point I had respectively. Values of them were already set according to
implemented integration of sine components method. experimental conditions. Normalization was a pixel-wise
Therefore further steps according to this method are given operation which did not change the clarity of the ridge and
below: valley structures. If normalization was performed on the entire
6. Value å was computed, an image containing only the sin image, then it could not compensate for the intensity
component of O´. variations in different parts of the image due to the elastic
nature of the finger. Separate normalization of each individual
sector alleviated this problem. Fig. 6 shows normalized image.
7. A label image A was used to indicate the reference point. Gabor filters optimally capture both local orientation and
For each pixel (i,j) in å, pixel intensities (sine component of frequency information from a fingerprint image. By
the orientation field) were integrated in regions and as
shown in Fig. 4 and the corresponding pixels were assigned
in A,the value of their difference was calculated as :

The regions and (see Fig. 4) were determined
empirically by applying the reference point location algorithm Fig. 4 Regions for integrating å pixel intensities for A(i,j)
over a large database. The geometry of these regions was
designed to capture the maximum curvature in concave ridges.
8. Maximum value in A was found out and its co- ordinates
were assigned to the core point [2]. By repeating the steps
fixed number of times for different window sizes, accurate
core point was calculated. However, this method was not
able to find out correct core point in an arch type of
singularities. According to some authors it’s beneficial to
combine two-three methods for detecting accurate core point
as in [9].
B. Tessellation of Region of Interest
Fig. 5 Core point (×), Region of interest and 80 sectors
After finding out the core point, the circular region around Superimposed on a fingerprint
this core point was tessellated into sectors as in [2].I used 5
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© 2011 ACEEE
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tuning a Gabor filter to specific frequency and direction, the VI .MATCHING
local frequency and orientation information can be
obtained..Thus, they are suited for extracting texture Fingerprint matching was based on finding the Euclidean
information from images. An even symmetric Gabor filter distance between the corresponding Finger Codes. The
had the following general form in the spatial domain as in translation invariance in the Finger Code was established by
[4],[6]: the reference point. Approximate rotation invariance was
achieved by cyclically rotating the features in the Finger Code
itself. For each fingerprint 5 templates were stored in the
database. Test fingerprint template was matched with all the
5 templates of each fingerprint and scores were noted [2].The
minimum score corresponded to the best alignment of the
two fingerprints being matched. If the Euclidean distance
where f was the frequency of the sinusoidal plane wave along between two feature vectors was less than a threshold, then
the direction è from the x-axis, and were the space the decision that “the two images come from the same finger”
constants of the Gaussian envelope along x’ and y’ axes, was made, otherwise a decision that “the two images come
respectively.It’s beneficial to set the filter frequency f to the from different fingers” was made.
average ridge frequency ( 1/K), where K was the average
inter-ridge distance. I used eight different values for è (0,
22.5,45, 67.5, 90, 112.5, 135, and 157.5) with respect to the x-
axis. The normalized region of interest (see Fig.6) in a
fingerprint was convolved with a 0Ú-oriented filter
accentuates those ridges which are parallel to the x-axis and
smoothes the ridges in the other directions. Filters tuned to
other directions work in a similar way. These eight
directional-sensitive filters captured most of the global ridge
directionality information as well as the local ridge Fig.7 Filtered Images (a) 0Ú (b) 22.5Ú similarly up to
characteristics present in a fingerprint. Fig. 7 shows filtering 157.5Ú.While four directions are sufficient for classification; eight
directions are needed for fingerprint identification.
in different directions, as in [2], [4].

V. FEATURE VECTOR

Let be the è-direction filtered image for sector
.Now,
, ª {0,1,…,79} and è ª {0Ú,……,157.5Ú},the feature
value , ,was the average absolute deviation from the mean
defined as :

Fig.8 Examples of 640-dimensional feature vectors: (a) First
Fig. 6 Fingerprint Images: (a) Area of Interest (b) Normalized
impression of finger 1, (b) second impression of finger 1, (c) Finger
Image Code of (a), (d) Finger Code of (b)
Since the template generation for storage in the database
was an off-line process, the verification time still dependent
on the time taken to generate a single template.
where was the number of pixels in and was the mean
of pixel values of in sector .The average absolute VI. EXPERIMENTAL RESULTS
deviation of each sector in each of the eight filtered images
For performing the whole procedure I used FVC 2000
defined the components of our feature vector. In this way a
database. In this database there were eight fingerprint scans
640-dimensional feature vectors were formed. Fig. 8 shows
per person and total there are 80 scans of 10 persons. When
examples of 640-dimensional feature vectors for fingerprints.
the Gabor Filter-Based Fingerprint Identification was applied
on this database I got overall 98.22% accuracy. The accuracy
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was measured in terms FRR (False Rejection Rate) and FAR REFERENCES
(False Acceptance Rate).That’s why this method was found
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based fingerprint matching”, IEEE Transactions on Image
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Identification. Gabor filters are characterized by frequency [4] M.Huppmann,” Fingerprint recognition by matching of
and orientation a component that’s why they are perfectly gabor filter-based patterns”, unpublished.
suitable for fingerprint Identification. The primary advantage [5] M.Umer Munir and Dr. M.Y. Javed,” Fingerprint matching
of this approach was its computationally attractive matching/ using gabor filters”, unpublished.
indexing capability. For instance, if the normalized (for [6] J.R.Movellan,”Tutorial on gabor filters”, unpublished.
orientation and size) Finger Codes of all the enrolled [7] M. Liu, X. Jiang , A. C . Kot,” Fingerprint reference–
point detection”, EURASIP Journal on Applied Signal
fingerprints were stored as templates, the identification
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effectively involves a “bit” comparison. As a result, the [8] H. B. Kekre,V.A. Bharadi,”Fingerprint core point detection
identification time would be relatively insensitive to the detection algorithms using orientation field based multiple
database size. The accuracy achieved in terms of FRR and features”,International Journal of Computer Applications vol.1,
FAR was 98.22%.Therefore the whole discussion in this paper pp. 97- 103.
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based system. for fingerprint core point detection”,unpublished.

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© 2011 ACEEE
DOI: 01.IJNS.02.03.159

A Novel Approach to Fingerprint Identification Using Gabor Filter-Bank

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