In this paper, an attempt has been made to extract texture features from facial images using an improved method of Illumination Invariant Feature Descriptor. The proposed local ternary Pattern based feature extractor viz., Steady Illumination Local Ternary Pattern (SIcLTP) has been used to extract texture features from Indian face database. The similarity matching between two extracted feature sets has been obtained using Zero Mean Sum of Squared Differences (ZSSD). The RGB facial images are first converted into the YIQ colour space to reduce the redundancy of the RGB images. The result obtained has been analysed using Receiver Operating Characteristic curve, and is found to be promising. Finally the results are validated with standard local binary pattern (LBP) extractor.

1. Use of Illumination Invariant Feature Descriptor For
Face Recognition
Noorjahan Khatoon*
Dept. of Computer Engineering and General Science
Advanced Technical Training Centre (ATTC)
Bardang, East Sikkim, India
njk_gtk@yahoo.com
Mrinal Kanti Ghose
Dept. of Computer Applications
Sikkim University
Samdur, Tadong, Gangtok, East Sikkim, India
mkghose2000@yahoo.com
Abstract: In this paper, an attempt has been made to extract texture
features from facial images using an improved method of
Illumination Invariant Feature Descriptor. The proposed local
ternary Pattern based feature extractor viz., Steady Illumination
Local Ternary Pattern (SIcLTP) has been used to extract texture
features from Indian face database. The similarity matching
between two extracted feature sets has been obtained using Zero
Mean Sum of Squared Differences (ZSSD). The RGB facial images
are first converted into the YIQ colour space to reduce the
redundancy of the RGB images. The result obtained has been
analysed using Receiver Operating Characteristic curve, and is
found to be promising. Finally the results are validated with
standard local binary pattern (LBP) extractor.
Keywords—LBP; LTP; SIcLTP; ZSSD; face recognition;
texture feature.
I. INTRODUCTION
Humans often use faces to recognize individuals and
advancements in computing capability over the past few decades
now enable similar recognitions automatically [9]. Early face
recognition algorithms used simple geometric models, but the
recognition process has now matured into a science of
sophisticated mathematical representations and matching
processes [17]. The characteristic that makes it a desirable
biometric modality is its uniqueness, universality, acceptability
and easy collectability. Face recognition can be used for both
verification and identification. Its potentiality and applicability
in the areas of security and surveillance makes it more lucrative
to be studied as biometric modality. Also, its ease of acquisition
from a distance via non-contact offers an added advantage over
other biometric modalities.
Its use in biometric could provide access control to various
internet of things which are used to protect house, property,
child and non-adult population from dangerous predators and
illegal hazards.
An excellent survey of existing Face recognition technologies
and challenges is given by Li. et al [10]. The problems
associated with illumination, gesture, facial makeup, occlusion,
and pose variations adversely affect the recognition
performance. While Face recognition is non-intrusive, has high
user acceptance, and provides acceptable levels of recognition
performance in controlled environments, the robust face
recognition in non-ideal situations continues to pose challenges
[17]. This of course is minimized a little by 3D technologies
[11]. Sharma et al [11] have given a survey of different concepts
and interpretations of biometric quality. To deal with low-
resolution face problem, Choi et al [20] demonstrated that face
colour can significantly improve the performance compared to
intensity-based features. Experimental results show that face
colour feature improved the degraded recognition rate due to
low-resolution faces by at least an order of magnitude over
intensity-based features.
Ahonen et al [21] experimented with chromatic information
integrating them with an adaboost learner to address non
linearity in face patterns and illumination variations in training
databases for facial recognition. Uçar et al [3], presented colour
face recognition algorithm by means of fusing colour and local
information. Kalaiselvi et al [8] have made face recognition
more reliable under uncontrolled lighting conditions by
combining the strengths of robust illumination normalization,
local texture based face representations, distance transform
based matching and kernel based feature extraction and multiple
feature fusion.
II. CHALLENGES IN FACE AS A BIOMETRIC MODALITY
One of the biggest challenges faced by human beings is that if
the number of unknown faces is very large, it becomes very
difficult for anyone to correctly identify the faces [19].
International Journal of Computer Science and Information Security (IJCSIS),
Vol. 16, No. 3, March 2018
118 https://sites.google.com/site/ijcsis/
ISSN 1947-5500

2. In this area computers are quite efficient in terms of the high
memory space, computational speed, accuracy and diligence.
Some of the important challenges in face recognition are
described hereunder [16].
(i)Pose variation happening due to subject’s movements or
camera’s angle may result in deteriorating illumination
condition and thus affecting the accuracy of face recognition.
(ii)Face occlusion due to presence of beards, glasses or hats
causes high variability and poses hindrance in the feature
extraction of the important parts of face such as eyes, nose,
forehead and mouth. Face features can also be partially covered
by objects or other faces present in the scenes.
(iii) Facial expression may influence the quality of an image,
affecting the appearance of a face. Such situation also hampers
the illumination condition of the images in consideration.
(iv)Illumination variation due to non-uniform lighting
conditions may also pose a great challenge in facial recognition
system. The stark dazzle and glare makes the process of feature
extraction difficult leading to poor pattern identification.
III. IMPORTANT FEATURE EXTRACTION TECHNIQUES
Literature survey reveals that many recognition techniques
involving various methods of feature extraction for biometric
authentication have been devised over the years, but none of the
techniques proposed are 100% safe and accurate.
The major feature extraction techniques are
a) PCA based approach [4]
b) SIFT based approach [5] and
c) SURF based approach.[6]
Each of them is having their advantages and disadvantages.
Therefore further investigation into this field is a continued
effort.
IV. OBJECTIVE OF THE PRESENT STUDY
In this paper, an improved illumination invariant feature
descriptor has been investigated to extract the colour texture
features from facial imageries. Analysis of textures has been an
important factor in image processing having many applications
such as object recognition, remote sensing and content based
image retrieval tasks [2]. It is an integral part of machine vision
and texture classification and is the direct implication of object
recognition. The present study mainly exploits this issue.
A simple strategy which could be used to analyse image
texture is to find changes in texture on a sliding window.
Texture features are summed up as scalar values and features are
assigned to each of the image pixel pertaining to window
centres. For each pixel, a description of the ‘texture” depends on
the neighbouring pixels. Stochastic textures are usually natural
and consist of randomly distributed texture elements,
represented by lines or curves [22].
Most of the works that has been carried out so far pertains to
the spatial statistics of the image gray level which is closer to
the definition of texture.
The performance of different classifiers depends much on the
feature data that have been used. The Local Binary Pattern
(LBP) is considered to be simple yet efficient and less complex
in implementation [15] but has the weakness such as sensitivity
to noise. Very often LBP code defined over an image is used to
describe the texture as a histogram of that image [23].
2
1
0
, )(
p
P
P
RP xsLBP ∑
−
=
=
, cp ggxwhere −=,
⎩
⎨
⎧
<
≥
=
,0,0
,0,1
)(,
x
x
xSand
(1)
where, g and g ( = 0, − 1) denote the gray value
of the centre pixel and gray value of the neighbour pixel on a
circle of radius , respectively, and is the number of the
neighbours.
The Local ternary pattern (LTP) is a variant of Local
Binary Pattern and is found to be a very powerful feature
descriptor [15].
V. PROPOSED METHOD
The LBP operator has two major points of weaknesses;
firstly, if the images are deformed and the pattern is not
uniform, it misses the local structure as it fails to consider the
effect of centre pixel. Secondly, the flat image areas are having
all pixels approximately the same gray values, the LBP operator
will give some bits the value 0 and others the value 1, implying
noise being added to these areas. This makes the operator
unstable. Thus LBP operator becomes unsuitable for analyzing
these areas [14].
Tan and Triggs [15] presented a new texture operator
viz., Local Ternary pattern, which is more robust to noise. The
problem of noise in the LBP has been resolved by introducing a
user defined threshold say, t, to the central pixel and reassigning
pixel values in the interval (-1, +1).
International Journal of Computer Science and Information Security (IJCSIS),
Vol. 16, No. 3, March 2018
119 https://sites.google.com/site/ijcsis/
ISSN 1947-5500

3. One of the major challenges faced in object recognition is
illumination variation. Liao et al. [18] proposed an efficient
background subtraction framework that dealt with illumination
variation, in which a pixel wise background subtraction
algorithm with local patterns on monocular grey scale video
sequences is used.
This present work is motivated by the same concept with
improvement used in case of object recognition. The
illumination invariant descriptor viz., SIcLTP has an
improvement over LBP/LTP wherein, the constant value of
LTP for obtaining thresholded ternary output is replaced with a
value proportional to the intensity of the central pixel which is a
predefined scale factor, indicating how much of the central
pixel’s intensity can be tolerated. Also the radius parameter of
SIcLTP is determined by the value of central pixel making it
illumination invariant. SIcLTP has an edge over LTP in terms of
advantages offered which are:
1. The operator is computationally simple and efficient.
2. The presence of a tolerant value makes it robust in case
of noisy images.
3. The scale invariance property makes it more robust to
illumination changes.
Mathematically, given any pixel location, (xc, yc), SIcLTP
encodes it as
∑
−
=
=
1
0
),(),(,
N
b bpcptscycxRN
tSIcLTP (2)
where,
Pc is the intensity value of the centre pixel,
Pb is that of its N neighborhood pixels
N neighborhood
R radius
∑ denotes concatenation operator of binary strings
t is a scale factor indicating the comparing range
Since each comparison can result in one of three values, SIcLTP
encodes it with two bits, and St is a piecewise function defined
as
⎪
⎩
⎪
⎨
⎧
−<
+>
=
.,00
)1(,10
)1(,01
otherwise
PtPif
PtPif
cb
cb
ts (3)
VI. FACIAL FEATURE EXTRACTION
In this paper, the experiment has been conducted using the
Indian face database by Jain and Amitabha [12]. Ten instances
of thirty male and female facial images making it a total of three
hundred facial images have been considered for extracting
texture features using a Local Ternary Pattern based texture
feature descriptor named Steady Illumination colour Local
Ternary Pattern (SIcLTP)as described in Equation (2) and (3)
above. It is worth mentioning that the application of the said
technique had yielded promising results for Iris images [1]. .
After extracting the features from Faces using SIcLTP, the
similarity and dissimilarity between the equal sized images have
been tested using the concept of Zero Mean Sums of Squared
Differences (ZSSD) proposed by Patil et. al [7].
VII. EXPERIMENTAL RESULTS AND DISCUSSION
The experimental results obtained for the above mentioned
facial database is plotted in the form of Receiver Operating
Characteristic (ROC) curve as the measure of the discriminating
power of the classifier or object recognizer, which in turn
describes the accuracy of a test to discriminate match and
mismatch cases [13]. Some of the sample input images from the
database are depicted in Fig 1 below.
Fig 1 Sample input Face images from the database
Fig. 1: Sample face images from the database
The samples of extracted features using the proposed
descriptor viz., SIcLTP, from the facial images are shown in Fig
2 below.
Fig 2 Face features extracted with proposed SIcLTP operator
International Journal of Computer Science and Information Security (IJCSIS),
Vol. 16, No. 3, March 2018
120 https://sites.google.com/site/ijcsis/
ISSN 1947-5500

4. Validation of the result obtained has been carried out for
the same database using LBP as a feature descriptor as
mentioned in Equation (1) above. The process of finding the
similarity match is also kept same using ZSSD in this case also.
The samples of the LBP extracted features are shown
below in Fig 3.
Fig 3 Face features extracted using LBP
The image similarity matching was done at random,
picking any image from the database and matching that image
with other images in the database at random. The sum of squared
differences results in a scalar value which denotes how closely
the images compared are similar. The scalar value 0 indicates the
exact and symmetrical match and the lowest values indicate the
closest and correct matches.
The ROC curves used to plot the results obtained is
shown below in Fig 4 for SIcLTP and Fig 5 for LBP.
Fig 4 ROC curve using SIcLTP
Fig 5 ROC curve using LBP
The tabulation for comparison of the accuracy with respect the
SIcLTP and LBP method used has been shown inTable1 below.
TABLE I. COMPARATIVE RECOGNITION ACCURACY
The comparison of recognition accuracy makes it evident that
the SIcLTP performs better than LBP, as the recognition
accuracy using SIcLTP is much higher than using LBP.
VIII. CONCLUSION
In this paper, the experiments have been conducted for Indian
Face Database by converting the RGB colour space of the data to
YIQ colour space. The proposed SIcLTP operator has been
applied. The recognition accuracy has been measured by using
ZSSD and the efficiency of the proposed descriptor has been
evaluated by using ROC curve. The results obtained are depicted
in Table and Figures above. It is worth mentioning that the
accuracy of the proposed descriptor is 82% in comparison to
LBP being 51% only. The experiment conducted thus
demonstrated the effectiveness of the operator SIcLTP, as a
feature extractor for Face modality. Further, the Face modality
could be used in context to the fusion of modality with other
biometric traits to further enhance the accuracy in a multimodal
scenario.
Method AUC
Correct matches
in %
SIcLTP 0.753 82.2%
LBP 0.575 51.1%
0
20
40
60
80
100
0 20 40 60 80 100
100-Specificity
Sensitivity
0
20
40
60
80
100
0 20 40 60 80 100
100-Specificity
Sensitivity
International Journal of Computer Science and Information Security (IJCSIS),
Vol. 16, No. 3, March 2018
121 https://sites.google.com/site/ijcsis/
ISSN 1947-5500

5. REFERENCES
[1] Noorjahan Khatoon, Mrinal K Ghose, Steady Illumination Color Local
Ternary Pattern as a Feature Extractor in Iris Authentication,
Proceedings of SAI Intelligent Systems Conference (Intellisys) 2016,
Lecture notes in Networks and Systems, Computational Intelligence,
Springer International Publishing, Vol. 2, pp. 966-973, 2016.
[2] P. Perner, Cognitive Aspects of Object Recognition - Recognition of
Objects by Texture, 19th International Conference on Knowledge based
and Intelligent Information and Engineering Systems, Procedia Computer
Science, Elsevier Publication, Vol. 60, pp. 391-402, 2015
[3] A. Uçar, Color Face Recognition Based on Steerable Pyramid Transform
and Extreme Learning Machines, Research Article, The Scientific World
Journal Volume, Hindawi Publishing Corporation, pp.1-15 , 2014
[4] Sudeep Thepade, Rik Das and Saurav Ghose, Feature Extraction with
Ordered Mean Values for Content Based Image Classification, Advances
in Computer Engineering, Hindawi Publishing Corporation, Vol. 15,
pp.1-6, 2014
[5] Minal Mun and Prof. Anil Deorankar, Implementation of Plastic Surgery
Face Recognition using Multimodal Biometrics Features, (IJCSIT), Vol.
5, Issue 3, pp. 3711-3715, 2014
[6] Priyanka and Y. Singh, A study on facial feature extraction and facial
Recognition Approaches, International Journal of Computer Science and
Mobile Computing, Vol. 4, Issue 5, pp. 166-174, 2014
[7] S. Patil, J. S. Nadar, J. Gada , S. Motghare and S. S Nair, Comparison of
Various Stereo Vision Cost Aggregation Methods, International Journal
of Engineering and Innovative Technology, (IJEIT) Volume 2, Issue 8,
pp. 222-226, 2013
[8] P. Kalaiselvi and S. Nithya, Face Recognition System under Varying
Lighting Conditions, IOSR Journal of Computer Engineering (IOSR-
JCE), Vol. 14, Issue 3,pp. 79-88, , 2013
[9] Tian J. Hu, Q. Ma, M. X. Ha, An Improved KPCA/GA-SVM Classification
Model for Plant Leaf Disease Recognition, Journal of Computational
Information Systems, Binary Information Press, Vo. 8, Issue 18, pp.
7737-7745, 2012
[10] Stan Z. Li, Face Recognition: Methods and Practice, CBSR and NLPR,
ICB Tutorial Delhi, India, pp.1-186, 2012
[11] P. B. Sharma and M. M. Goyani , 3D Face Recognition Techniques - A
Review, International Journal of
Engineering Research and Applications (IJERA) Vol. 2, Issue 1, pp.787-
793, 2012
[12] Jain Vidit and Mukherjee Amitabha, The Indian Face Database, IIT
Kanpur, 2002, Accessed/Downloaded January 2012
[13] Z. Zhang and Y. Huang, A Linear Regression Framework for the
Receiver Operating Characteristic (ROC) Curve Analysis, Open Access
Research Article in Biometrics & Biostatistics, Vol. 3, issue 2, pp. 2-7,
2012
[14] C. Zhu and R. Wang, Local Multiple Patterns based Multiresolution
Gray-Scale and Rotation Invariant Texture Classification, Information
Sciences, Vol. 187, pp. 93-108, 2011.
[15] X. Tan and B. Triggs, Enhanced Local Texture Feature sets for Face
Recognition under Difficult Lighting Conditions, IEEE Transactions on
Image Processing, Vol. 19, Issue 6, pp. 1635-1650, 2010
[16] Biometrics Market Intelligence http://www.Biometricsmi.com. Accessed
January 2010
[17] P. Buyssens and M. Revenu , Fusion Levels of Visible and Infrared
Modalities for Face Identification, BTAS, Washington, US, Vol. 6,
pp.1-6, 2010
[18] S. Liao, G. Zhao, V. Kellokumpu, M. Pietikainen, and S. Z. Li, Modelling
Pixel Process with Scale Invariant Local Patterns for Background
Subtraction in Complex Scenes, Center for Biometrics and Security
Research & National Laboratory of Pattern Recognition, Institute of
Automation, Chinese Academy of Sciences, Machine Vision Group,
University of Oulu, Finland, pp.1-6, 2008.
[19] Annu Rev Neurosci., Mechanism of face perception, doi:
10.1146/annurev.neuro.30.051606.094238, pp. 411–437, 2008.
[20] J. Young Choi, S. Yang, Y. M Ro and K. N Plataniotis, Color Effect on
the Face Recognition with Spatial Resolution Constraints, Tenth IEEE
International Symposium on Multimedia, IEEE Computer Society, pp.
294-301, 2008
[21] T. Ahonen, A. Hadid, and A. Pietikainen, Face Description with Local
Binary Patterns: Application to Face Recognition, IEEE TPAMI, Vol 28,
Issue 12, pp.1-15, 2006
[22] A. Materka and M. Strzelecki, Texture Analysis Methods - A Review,
Technical University of Lodz, Institutes of Electronics, Cost B11 Report,
Brussels, pp. 1-33, 1998
[23] T. Ojala, M. Pietikäinen and D. Harwood, A Comparative Study of
Texture Measures with Classification based on Feature Distributions,
Pattern Recognition. Vol. 29(1), pp. 51–59, 1996
International Journal of Computer Science and Information Security (IJCSIS),
Vol. 16, No. 3, March 2018
122 https://sites.google.com/site/ijcsis/
ISSN 1947-5500