Performance Enhancement of Minutiae Extraction Using Frequency and Spatial Domain Filters R.Anandha Jothi Research Scholar Department of Computer Applications Alagappa University Karaikudi. TamilNadu, India. [email protected]1 Dr.V.Palanisamy Professor & Head Department of Computer Applications Alagappa University Karaikudi. TamilNadu, India. [email protected]2 Abstract— Minutiae based feature extraction method is an important system for person identification. Yet spurious and false minutiae are often occurring. The fingerprint images are hardly in good quality. They may be corrupted due to deviation in skin condition (dry, wet) and skin impression. Therefore, fingerprint image enrichment techniques are working prior to minutiae extraction to accomplish more reliable estimation of minutiae positions. So to overcome these issues, in this proposed work, spatial and frequency domain filters are effectively implemented in fingerprint image pre-processing processes individually and followed by minutiae are extracted. Subsequently fingerprint image quality is verified in terms of MSE, PSNR and SSIM and found to be good for AMF. Average value of performance evaluation in minutiae extraction is found be 0.31and 0.10 for FFT and AMF respectively. Hence FFT can be used effectively in fingerprint minutiae extraction in person authentication. Keywords— Fingerprint; minutiae extraction; Fast Fourier Transform; spatial domain filter I. INTRODUCTION Most of the person identification systems used biometric characteristics such as behavioral and physical traits of a person. This supports identification of individual among groups of others. The fingerprint is one of the most reliable biometric features. As it remains unique for a specific individual and has also been verified to be more perfect. Therefore, fingerprint helps to be the maximum acceptable, widespread and matured biometric characteristics. A fingerprint is concerned with pattern of interleaved ridges and valleys. The group of local characteristic and their relationship are determining the individuality and invariant features of the fingerprint. The most often used fingerprint features are minutiae, Minutiae has two significant characteristics such as ridge ending and ridge bifurcation that organize a fingerprint pattern. The fingerprint feature extraction process carried out by enhancement or pre-processing, minutiae detection and extraction. Therefore, minutiae based fingerprint authentication method offers reasonable identification speed and accuracy. Also, minutiae based feature extraction method is well acknowledged around the crime and forensic investigation organizations of maximum countries. The minutiae map contains around 70 to 100 minutiae points and matching accuracy is reduced while the size of the database is growing up. Hence, it is unavoidable to make the size of the fingerprint feature code to be lesser than possible; finally the identification may be considerably faster and easier.Automatic fingerprint identification system (AFIS) for minutiae based technique usually consists of the following phases (i) Image pre-processing (ii) Feature detection and extraction. In this work a comparative study was conducted on the Performance Evaluation (PE) of extracted minutiae from the two approaches such as frequency and spatial filters. The rest of the paper is planned as follows: Section II describes Frequency domain filter, i.e. fast Fourier Transformation (FFT) method for fingerprint enhancement. Section III presents the methods of spatial nonlinear filters (Min/Max, midpoint, Adaptive Median Filters (AMF)) for fingerprint enhancement. Section IV The minutiae extraction process were deliberated. Section V gives experimental results and discussions are reported. Section V provides conclusion of this paper. II. RELATED WORK Fingerprint image enhancement or pre-processing techniques are studied by various researchers for removing noise and other ambiguous effects, Chaohong Wu [1] et.al. Proposed directional median filters to eliminate noise and spurious signals for fingerprint image enhancement. Shlomo Greenberg et al. [2] studied two different methods for removing noise and improve the quality of fingerprint images. The first method carried out by wiener filtering for binarization and thinned image. The second method uses an anisotropic filter for direct grayscale enhancement. Both methods were improving the International Journal of Pure and Applied Mathematics Volume 118 No. 7 2018, 647-654 ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version) url: http://www.ijpam.eu Special Issue ijpam.eu 647
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International Journal of Pure and Applied Mathematics Special Issue
648
(d) Extracted Minutiae image
B. Spatial Filtering
Further Spatial domain filtering based enhancement
method was used for pre-processing, the outcome of filtering
produce faithful minutiae [13]. Most of the filters are used for
image noise removal. Which is used for different task i.e.
noise reduction, interpolation, re-sampling and blurring.
Blurring is used to remove small dots and unwanted structures
from an image earlier to large object extraction. The selection
of filter depends upon the type and amount of noise presented
in an image subsequently those dissimilar filters can remove
different types of noise effectively. The spatial domain filters
has two kinds, such as linear and Non-linear filters, in this
work we have achieved by Non-linear Min/Max, Midpoint
filter and Adaptive Median filters (AMF).Non-linear filters
exhibit well performance than linear filters [14].The non-
linear filters functionality is based on the ranking of pixels
enclosed in the image area covered by the filter, and then
replaces the value of middle pixel with the value determined
by the ranking result. The type of spatial domain filters as
follows.
C. Min and Max Filter
The smallest and the largest value within the pixel values
are selected by the minimum and maximum filter. In this
process, the maximum and minimum intensity values are
found within a window of certain pixels. The output remains
unchanged when the central pixel lies within the intensity
range of its neighbors. If the central pixel is greater than the
maximum value within that window, then it is set to the
maximum value and if it is less than the minimum value than
it takes the minimum value to itself [15]. The min/max filter
can be represented by the following equation (4) and (5)
𝑓 𝑥, 𝑦 = max(𝑠,𝑡)∈𝑆𝑥𝑦
{𝑔 𝑠, 𝑡 } … (4)
𝑓 𝑥,𝑦 = min(𝑠,𝑡)∈𝑆𝑥𝑦
{𝑔 𝑠, 𝑡 } … (5)
D. Adaptive Median Filter (AMF)
The AMF is used to determine which pixels in an image
have been pretentious by impulse noise. The AMF categorizes
pixels as noise and then matching each pixel in the given
image to it’s around neighbor pixels. The size of the
neighborhood is modifiable, In addition to the threshold for
the comparison. A pixel that is dissimilar from a majority of
its neighbors, in addition to not structurally align with these
pixels to which it is similar, is called as impulse noise. That
kind of noise pixels is replaced by the median pixel value of
the pixels in the neighborhood that have passed the noise
labeling test.
Notation
𝑍min = 𝑆𝑥𝑦 is the minimum\ lowest grey level value .
𝑍𝑚𝑎𝑥 = 𝑆𝑥𝑦 is the maximum\ highest grey level value.
𝑍𝑥𝑦 = (𝑥,𝑦) grey level at the subject matter
coordinates.
𝑍𝑚𝑒𝑑 = is the maximum possible 𝑆𝑥𝑦window size.
Algorithm
We should analyze the following definition of AMF
at two levels. Let us the function A and B.
Level A: A1 =𝑍𝑚𝑒𝑑 − 𝑍min
A2 =𝑍𝑚𝑒𝑑 − 𝑍max
If A1 > 0 and A2 < 0 then do to definition B.
Level B: B1=𝑍𝑥𝑦 − 𝑍min
B2=𝑍𝑥𝑦 − 𝑍max
If B1 > 0 and B2 < 0, output 𝑍𝑥𝑦 .
Else output 𝑍𝑚𝑒𝑑 .
From the above level A and B of AMF effectively to eliminate
the impulse noise .The definition of Level A and B are given
below.
Explanation of level A: To determine whether the output
value of the filter 𝑍𝑚𝑒𝑑 is in the noise or not If 𝑍min <
𝑍𝑚𝑒𝑑 < 𝑍max the 𝑍𝑚𝑒𝑑 value is not a noise value ant it
must be transmitted to the exit.
Explanation of level B: To determine whether 𝑍𝑥𝑦 𝑖𝑡self is
a noise level and a new value to be according to this. The
definition of the above algorithm that the median value of
level A is equal to the noise, in case similar this the window
size to be inspected will be changed and alternative median
value will be calculated. The above process will be continued
up to the median value comes different between maximum or
minimum value. However, this can’t guarantee that the
obtained value is not noise. Nevertheless, dependent on the
window size the probability of finding a noise value will be
minimized. While increase the widow suppresses the noise to
an excessive extent, simultaneously, proportion to its size.
E. Midpoint Filter
The midpoint filter is used for blurring the image by
replacing it with the average of the highest intensity pixel and
the lowest intensity pixel within the specific window. Median
filter can be signified by the below equation (6).
𝑓 𝑥, 𝑦 =1
2max
(𝑠,𝑡)∈𝑆𝑥𝑦{𝑔 𝑠, 𝑡 + min
(𝑠,𝑡)∈𝑆𝑥𝑦{𝑔 𝑠, 𝑡 } … (6)
F. Minutiae Extraction
Once the frequency and spatial domain filtering has been
applied for enhancing the ridge pattern, then some more steps
are performed for minutiae extraction. Such as Binarization
and Thinning, Binarization of the image obtained is done
keeping the threshold as zero [16, 17]. A value of
representation that the pixel is white and a value of zero
indicate the pixel to be black. A threshold value is set for each
pixel in the image. Those pixel values which are smaller than
International Journal of Pure and Applied Mathematics Special Issue
649
the threshold is set to zero and the pixel values which are
greater than the threshold is set to one. The image produced is
in binary form. Thinning operation is done on the binary
image obtained from the previous step. Thinned ridge lines are
obtained using morphological thinning operator bwmorph [18,
19]. Finally minutiae extraction is done on the thinned image.
This process is done by using a 3x3 window to examine the
local neighborhood of each ridge pixel in the image. The
minutiae extraction is based on crossing number concept.
G. Minutiae Extraction Using Crossing Number (CN)
The crossing number (CN) at a point P is defined as half of the cumulative successive differences [19, 20] and is expressed as follows in equation (7).
CN =1
2 |Pi − Pi+1|
8
𝑖=1
(7)
Where Pi is the value in the neighborhood of P. Pi= (0,1) and I has a period of 8, that is P9=P1.For any pixel P, we consider the 8 neighboring pixels in a 3x3 neighborhood, each of which can take a value of either 1 or 0 as follows: CN has the following properties.
CN Property
0 Isolated Point
1 Ridge Ending Point
2 Continuing Ridge Point
3 Bifurcation Point
4 Crossing Point
The end points and branching points or minutiae are detected using the above mentioned properties of CN. The skeleton image is scanned for detecting the minutiae. It has been found that for ―valid‖ bifurcation points an additional condition of a number of neighbors equal to three is required.
VI. PERFORMANCE EVALUATION (PE)
To evaluate the performance of enhancement filters, the
perceived minutiae are compared with a set of minutiae
attained from the same fingerprint by a human expert. The
performance evaluation (PE) is expressed by the following
equation (8).
𝑃𝐸 =𝑀𝑝−𝑀𝑚 −𝑀𝑠
𝑇𝑜𝑡𝑎𝑙 𝐻 (8)
Wherever Mp is the number of pairs matched within the
enhanced image, Mm and Ms Represent the number of
dropped, spurious minutiae respectively, and TotalH is denoted
as the number of minutiae extracted by the human experts.
The maximum value of PE=1, All the total number of
minutiae are correctly paired with the corresponding detected
minutiae and there are no missing minutiae (Mp=TotalH and
Mm=Ms=0) respectively [21, 22]. Hence all the detected
minutiae are matched or paired. A large value of PE for a
fingerprint image denotes that the enhancement filters have
done a good performance on the image.
A. Quality Measure
After preprocessing the fingerprint image quality was
measured by various quality measurement techniques. Those
techniques are used to estimate the enhancement effect. The
most universally accepted objective measures are i) Structural
Similarity Index Measure (SSIM) ii) Peak signal to noise ratio
(PSNR) and iii) Mean Squared Error (MSE).
B. Structural Similarity Index Measure (SSIM)
The structural similarity index method is based on
measurement of three components such as luminance,
structure and contrast comparison. SSIM process is combined
with these separate components. The structural similarity
amongst the input image x and enhanced image y [23, 24, 25].
SSIM was calculated by the equation (9).
Where 𝜇𝑥 , 𝜇𝑦 are means and𝜎𝑥2, 𝜎𝑦
2 are variances of x and y
respectively, covariance of x, y is 𝜎𝑥 ,𝜎𝑦
and 𝐶1,𝐶2 are
adaptable constants, and L is the utmost possible value of x.
The input fingerprint images from FVC2004 DB3 database
was taken for measuring the SSIM index between original and
enhanced images.
C. Mean Squared Error (MSE)
MSE is calculated by an average squared intensity of the
original and resultant image pixels [26]. There was computed
by the equation (10). Here e (m, n) is error difference between
the original and the distorted images.
𝑀𝑆𝐸 =1
𝑁𝑀 𝑒(𝑚,𝑛) 2
𝑁−1
𝑛=0
(10)
𝑀−1
𝑚=0
D. Peak Signal to Noise Ratio (PSNR)
SNR is a mathematical measure of image quality based on
the pixel difference between input and resultant images. The
SNR to measure the quality of the reconstructed image
compared with the original image. Where S=255 for an 8-bit
pixel image. The PSNR is fundamentally the SNR while all
pixel values are equivalent to the maximum possible value
[27]. PSNR value was calculated by the given equation (11).
𝑃𝑆𝑁𝑅 = 10𝑙𝑜𝑔𝑆2
𝑀𝑆𝐸 (11)
VII. RESULT AND DISCUSSION
A. Quality Metrics
To measure the quality of frequency and spatial filter
based on enhanced fingerprint image. Yet there are many
techniques to evaluate the enhanced fingerprint image quality
such as MSE, PSNR, SSIM that indices depict in table 1 to 4
.The comparison of filters explained by charts shown in fig 3,4
and 5 respectively. The AMF based PSNR and SSIM values
are improved and the value of MSE reduced to compare with
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650
other filtering method. AMF based enhanced PSNR, SSIM
indices attains the maximum possible values against other
filtering methods. This clearly indicates that the AMF method
enhances gives a better quality fingerprint image as compared
to other filters.
Table 1. Quality measures for min\max filters.
Finger print image Min\Max Filters
DB2 MSE PSNR SSIM
DB3_B_102_7.tif 198.329 22.3152 0.8365
DB3_B_103_5.tif 117.386 24.4153 0.8591
DB3_B_104_7.tif 97.567 26.4695 0.8771
DB3_B_105_2.tif 196.562 22.5421 0.8382
DB3_B_106_1.tif 190.505 22.0283 0.8241
DB3_B_107_3.tif 225.300 23.1250 0.8525
DB3_B_108_5.tif 250.568 20.4862 0.8291
DB3_B_109_7.tif 230.021 21.3549 0.8328
DB3_B_110_8.tif 210.185 20.3110 0.8152
DB3_B_110_9.tif 197.574 21.3841 0.8388
Table 2. Quality measures adaptive median filters.
Finger print image Adaptive Median Filter
DB2 MSE PSNR SSIM
DB3_B_102_7.tif 98.7945 37.1524 0.9897
DB3_B_103_5.tif 94.8033 40.4026 0.9952
DB3_B_104_7.tif 83.1192 40.3852 0.9912
DB3_B_105_2.tif 88.3536 37.2702 0.9857
DB3_B_106_1.tif 100.2391 36.1271 0.9891
DB3_B_107_3.tif 110.3678 35.2491 0.9754
DB3_B_108_5.tif 96.9082 35.0842 0.9711
DB3_B_109_7.tif 90.2107 36.2341 0.9823
DB3_B_110_8.tif 89.1081 33.1782 0.9701
DB3_B_110_9.tif 101.4592 35.0247 0.9714
Table 3. Quality measures for Midpoint
Finger print image Midpoint
DB3 MSE PSNR SSIM
DB3_B_102_7.tif 220.235 21.2215 0.8168
DB3_B_103_5.tif 190.544 21.4356 0.7582
DB3_B_104_7.tif 160.236 22.3548 0.8971
DB3_B_105_2.tif 223.225 19.6544 0.878
DB3_B_106_1.tif 230.754 19.2756 0.802
DB3_B_107_3.tif 252.184 21.4599 0.8576
DB3_B_108_5.tif 263.698 18.415 0.8025
DB3_B_109_7.tif 245.541 17.3542 0.7897
DB3_B_110_8.tif 253.145 19.3633 0.7928
Table 4. Quality measures for FFT
Finger print image FFT
DB3 MSE PSNR SSIM
DB3_B_102_7.tif 128.327 25.3571 0.9728
DB3_B_103_5.tif 115.321 25.5786 0.9835
DB3_B_104_7.tif 121.604 26.6036 0.9615
DB3_B_105_2.tif 160.596 24.5242 0.9677
DB3_B_106_1.tif 135.448 24.8351 0.9782
DB3_B_107_3.tif 112.574 25.5623 0.9736
DB3_B_108_5.tif 134.553 25.1203 0.9685
DB3_B_109_7.tif 130.788 25.4128 0.9745
DB3_B_110_8.tif 157.752 24.5531 0.9352
B. Performance Evaluation
To compare the performance of both filters based on
extracted minutiae. The input image was selected from a
standard fingerprint database FVC2004 of DB2 & DB3. Table
5 & 6 depict the maximum and minimum value of PE of FFT
and AMF for this data set are 0.43- 0.11 and 0.21- 0.03,
similarly with an average value of PE is 0.31 to 0.10
respectively. The PE value calculated more than 100
fingerprint images. Hence, Table 5 & 6 shows only 6 value
those values are randomly chosen based on the number of
spurious minutiae. Such minutiae are grouped by average
(between 13 to 15), below average (between 11 to 12) and
above average (between 16 to 17). The statistical comparison
of those filters, FFT based PE value is much better than AMF
based PE value.
Table 5. PE value for FVC2004 DB2& DB3 database of five
fingerprint images for FFT filtering based extracted minutiae.
Fingerprint image T Mp M
Ms PE d e
DB2_B_101_1.tif 30 28 2 1 17 0.30
DB2_B_106_3.tif 33 28 4 3 11 0.39
DB3_B_110_1.tif 26 25 7 2 15 0.11
DB3_B_101_3.tif 32 29 3 2 12 0.43
DB2_B_109_7.tif 23 22 4 3 13 0.21
DB3_B_105_2.tif 37 35 2 3 17 0.43
Average PE value 0.31
Table 6. PE value for FVC2004 DB2 & DB3 database of five
fingerprint images for adaptive median filtering (AMF) based
extracted minutiae.
Fingerprint image T Mp M
Ms PE d e
DB2_B_101_1.tif 30 25 5 1 18 0.06
DB2_B_106_3.tif 33 26 6 3 13 0.21
DB3_B_110_1.tif 26 22 4 2 16 0.07
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Fig. 3 MSE value for
Spatial and frequency domain filters
Fig. 4 PSNR value for
Spatial and frequency domain filters
Fig. 5 SSIM value for
Spatial and frequency domain filters
DB2_B_110_1.tif
26 21 3 3 17 0.03
DB3_B_101_3.tif 32 25 7 2 15 0.09
DB3_B_105_2.tif 37 31 6 3 19 0.16
Average PE value 0.10
VIII. CONCLUSION
Fingerprint image enhancement has been successfully
studied using frequency and spatial domain filtering