Automatic detection of optic disc and blood vessels from retinal images using image processing techniques

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Issue: 03 | Mar-2014, Available @ http://www.ijret.org 300
AUTOMATIC DETECTION OF OPTIC DISC AND BLOOD VESSELS
FROM RETINAL IMAGES USING IMAGE PROCESSING TECHNIQUES
Oakar Phyo1
, AungSoe Khaing2
1
M.E Thesis Student, Department of Electronic Engineering, Mandalay Technological University, Mandalay, Myanmar
2
Associate Professor, Department of Electronic Engineering, Mandalay Technological University, Mandalay, Myanmar
Abstract
Diabetic retinopathy is the common cause of blindness. This paper presents the mathematical morphology method to detect and
eliminate the optic disc (OD) and the blood vessels. Detection of optic disc and the blood vessels are the necessary steps in the
detection of diabetic retinopathy because the blood vessels and the optic disc are the normal features of the retinal image. And also,
the optic disc and the exudates are the brightest portion of the image. Detection of optic disc and the blood vessels can help the
ophthalmologists to detect the diseases earlier and faster. Optic disc and the blood vessels are detected and eliminated by using
mathematical morphology methods such as closing, filling, morphological reconstruction and Otsu algorithm. The objective of this
paper is to detect the normal features of the image. By using the result, the ophthalmologists can detect the diseases easily.
Keywords: Blood vessels, Diabetic retinopathy, mathematical morphology, Otsu algorithm, optic disc (OD)
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1. INTRODUCTION
The visions of many people in the world are threatened by the
diabetic retinopathy. Diabetic retinopathy is the eye disease
that causes the blindness or blurs the visions. It arises due to
the high sugar level in the blood. According to the research,
the screening of diabetic retinopathy can reduce the risk of
blindness by 50% [1]-[2]. Therefore, early detection could
limit the severity of the disease and treating the disease more
efficiently. The optic disc detection is an important step to
identify the other fundus features. The optic disc can be seen
as the elliptical shape in the eye fundus image. Its size varies
from one person to another, between one-tenth and one-fifth
of the image [3]. In colour image, it appears as the bright
yellowish region as the exudates. The optic disc is the normal
feature of the image but the exudates are the abnormal case.
Detection the optic disc can be used to decrease the false
positive in the detection of the exudates [4]. And also the
detection of the blood vessels is as important as the detection
of the optic disc because the optic disc and the blood vessels
are the normal features of the image. Manual detection of
blood vessels is difficult since the appearance of blood vessel
in a retinal image is complex and having low contrast [5].
A number of methods for optic disc detection and blood
vessels detection have been published.Osarehet al. [6] located
the optic disc center by means of template matching and
extracted its boundary using a snake initialized on a
morphologically enhanced region of the optic disc. Lowell et
al. [7] also localized the OD by means of template matching as
well as also selected a deformable contour model for its
segmentation. Another deformable model-based approach was
presented in [8].Another template-matching approach for OD
segmentation is the Hausdorff-based template matching
presented by Lalondeet al. [9]. Initially, they determined a set
of OD candidate regions by means of multiresolution
processing through pyramidal decomposition. For each OD
region candidate, they calculated a simple confidence value
representing the ratio between the mean intensity inside the
candidate region and inside its neighborhood. The Canny edge
detector and a Rayleigh-based threshold were then applied to
the green-band image regions corresponding to the candidate
regions, constructing a binary edge map. As final step, using
the Hausdorff distance between the edge map regions and
circular templates with different radii, they decided the OD
among all the candidates.
There are some methods for blood vessels detection in retinal
fundus images such as region growing technique [10],
morphological and thresholding techniques [11], neural
network based approaches [12], statistical classification based
methods [13-14] and hierarchical methods[12]. This paper
presents the optic disc detection and blood vessels detection
techniques based on mathematical morphology on the fundus
images because it is very fast and requires lower computing
power. Therefore the system can be used even on a very poor
computer system.

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Fig -1: OD appearance. (a) Yellowish OD. (b) Brownish OD.
(c) Reddish OD. (d) Whitish OD.
The general flow chart for the optic disc detection and blood
vessels detection is shown in Fig.2
Fig -2: General flow chart for optic disc detection and blood
vessels detection
2. PRE-PROCESSING STAGE
2.1 Image Acquisition
All digital retinal images are taken from patients using the
non-mydriatic retinal fundus camera. The images are stored in
JPEG image format file (.jpg) and taken from "Eye and ENT
General Hospital (Mandalay)". In this research, the retinal
images are taken from the "Eye and ENT General Hospital
(Mandalay)" and also from the websites.
The original (RGB) image is transformed into appropriate
colour space for further processes. And then, filtering
technique is used to reduce the effect of noise. After using the
filtering technique, the noise such as salt and pepper noise are
removed from the image. Then contrast-limited adaptive
histogram equalization (CLAHE) is used for image
enhancement. Unlike histogram, it operates on small data
regions rather than the entire image. This function uses a
contrast-enhancement method that work significantly better
than regular histogram equalization for most images.
2.2 Converting Colors from RGB to HSI
In digital image, the input image can be the RGB (Red, Green,
and Blue) images or other. The RGB image can be described
as M x N x 3 array of colour pixels. In this paper, the RGB
input image is transformed into HSI colour space for further
processes. H component of each RGB pixel is obtained using
the following equation [15]
The saturation component is
Finally, the intensity component is
(a) Original image
(b) HSI image
Fig-3: shows the result of the converting colour from RGB to
HIS image. Fig.3 (a) is the original input image and Fig.3 (b)
is the HSI colour image.
Fundus image
Pre-Processing Stage
Optic Disc Detection
Blood Vessels Detection

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2.3 Filtering Techniques
Noise can cause the trouble in the detection of disease. The
noise contains in the image is reduced by using the filtering
technique such as median filter, averaging filter and wiener
filter.
2.3.1 Median Filter
The median filter is a non-linear filter type and which is used
to reduce the effect of noise without blurring the sharp edge.
The operation of the median filter is – first arrange the pixel
values in either the ascending or descending order and then
compute the median value of the neighborhood pixels.
Fig- 4: (a) Image with noise
Fig-4: (b) Result of median filter
2.3.2 Averaging Filter
Averaging filter is useful for removing grain noise from a
photograph. Each pixel gets set to the average of the pixels in
its neighborhood. The result of the averaging filter is shown in
Fig.5 (b).
Fig-5: (a) Image with noise
Fig-5: (b) Result of averaging filter
2.3.3 Wiener Filter
The wiener filter is used to minimize the mean square error
between input and output image. But the wiener filter requires
knowing the power spectral density of the original image
which is unavailable in practice. The result of the wiener filter
is shown in Fig.6 (b).
Fig-6: (a) Image with noise
Fig-6: (b) Result of wiener filter
According to the result images, the median filter is the best
suit to reduce the effect the noise. And also, it can reduce the
noise without blurring the edge. Therefore, the median filter is
chosen for the filtering purpose.
2.4 Image Enhancement
The result image of the median filter is enhanced by using the
histogram equalization technique. The histogram equalization
technique is used to overcome the uneven-illumination case.
There are two methods to enhance the image: Histogram
equalisation and Adaptive histogram equalisation.

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2.4.1 Histogram Equalisation
It enhances the contrast of the images by transforming the
values in an intensity image. The procedures of the histogram
equalisation are-
(i) Find the running sum of the pixel values
(ii) Normalise the values by dividing the total number of
pixels
(iii) Multiply by the maximum gray-level value and round the
value
The result of the histogram equalization is shown in Fig.7 (b)
Fig: 7- (a) Original Image
Fig-7: (b) Result of histogram Equalisation
2.4.2 Adaptive Histogram Equalisation
Unlike histogram, it operates on small data regions (tiles)
rather than the entire image. And also contrast enhancement
can be limited in order to avoid amplifying the noise which
might be presented in the image. So, Adaptive histogram
equalisation technique works significantly better than regular
histogram equalization for most images.
Fig-8: (a) Original Image
Fig-8: (b) Result of adaptive histogram equalization
According to results, the adaptive histogram equalisation
technique is used for image enhancement purpose.
3. OPTIC DISC DETECTION AND ELIMINATION
There are many methods to detect the optic disc and the blood
vessels for example; K-means clustering algorithm, Fuzzy C
means, Mathematical Morphology and so on. The
disadvantage of the Fuzzy C means ; for noisy images it does
not take into account spatial Information, which makes it
sensitive to noise & other image artifacts based on distribution
of pixel intensity, so it is sensitive to intensity variations in the
illumination.
The disadvantage of the K-means clustering algorithm is: K
the number of clusters must be determined; it does not yield
the same result each time the algorithm is executed.
But for the mathematical morphology, it doesn't have these
disadvantages and it doesn't need highly efficient computer, so
it can work on a poor computer. Therefore, it is suitable for
the rural area in developing country. So, the mathematical
morphology is chosen for the optic disc and blood vessels
detection.
3.1. Mathematical Morphology
The basic mathematical morphology operators include the
following:
 Dilation
 Erosion
 Closing
 Opening
Dilation adds pixels to the boundaries of objects in an image.
Erosion removes pixels on object boundaries.
The morphological open operation is an erosion followed by a
dilation, using the same structuring element for both
operations.
A◦B = (AΘB)⊕B
The closing operator is a dilation followed by erosion.
A●B = (A ⊕B)ΘB

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3.2. Thresholding
The Otsu's thresholding technique is applied to the image to
detect the desire area.
Equations of Otsu algorithm are
σ2
Between(T)=wB(T)wo(T)[µB(T)-µo(T)]2
wB(T) = , µB =
w0(T) = , µO=
 σ2
Between(T)= Between-class variance
 w=weight, B=background of the image, o=object of
image
 µ= combined mean,
 T= threshold value
The optic disc is the largest and brightest region of the image.
The optic disc detection is useful because it can reduce the
false positive detection of the exudates. Fig.5 shows the
general flow chart of the optic disc detection.
Fig-5: Flow Chart of Optic disc Detection
(a) (b)
(c) (d)
(e)
Fig-6: (a) Closing (b) Thresholding (c) Filling
(d) Reconstruction (e) Detected Optic disc
The results of the optic disc detection are shown in Fig.6 (a),
(b), (c), (d) and (e). Fig.6 (a) shows the result of the closing
operator. To remove the vessels, the closing (morphology)
operator is applied. When the closing operator is used, the
choice of structuring element is important. The closing is a
dilation followed by an erosion that joins the very close
objects together.Then, the result image is binarized by
thresholding using Otsu algorithm [16]. The result image is
shown in Fig.6 (b).The filling operator is applied to fill the
holes in the image and the result image is shown in Fig.6 (c).
The result image is reconstructed by using the morphology
reconstruction and is shown in Fig.6 (d). To detect the optic
disc region, the Otsu algorithm is applied on the difference
between the original image and the reconstructed image.The
optic disc detected area is shown in Fig.6 (e).
4. BLOOD VESSELS DETECTION AND
ELIMINATION
The blood vessels detection and elimination is also important
as the optic disc detection for further process because the optic
disc and the blood vessels are the normal features of the
images. The general flow chart of the blood vessels detection
is shown in Fig.7. To detect the blood vessels, first the input
image is converted into grayscale image due to strengthen the
appearance of the blood vessels. Then the median filtering and
the CLAHE techniques are used for reducing noise and image
enhancement purposes. Then, the closing and the filling
operators are used to close the same intensity values and fill
the holes in the vessels.
I(Difference)=ϕ(B1)
(I)-fill(I) [1]
RGB to HSI
Median Filter
Contrast-limited adaptive Histogram
Equalization
histogram equalizationClosing
Thresholding
Morphological
reconstruction
Binarization

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Where, B1 is the morphological structuring element.
Then the Otsu's thresholding technique is applied to the result
image to obtain the vessels area. The blood vessels detected
area is shown in Fig.8 (e).
I(vessels)=Thresholding(I(Difference)) [2]
Fig-7: Flow Chart of Blood Vessels Detection
(a) (b)
(c) (d)
(e)
Fig-8:(a) Closing (b) Filling (c) Difference (d) Thresholding
(e) Detected Blood Vessels
The results of the blood vessels detection are shown in Fig.8
(a), (b), (c), (d) and (e).The closing and the filling operators
are used to close the same intensity values and fill the holes in
the vessels. The result of the closing and the filling of the
images are shown in Fig.8 (a) and 8 (b). To get the blood
vessels area, Otsu algorithm is applied to the difference image
between the closing and the filling images. The result images
are shown in Fig.8 (c) and (d). The blood vessels detected area
is shown in Fig.8 (e).
5. DISCUSSION
In this paper, the mathematical morphology is applied to
detect the optic disc and the blood vessels. Detection of optic
disc and the blood vessels is the important step for further
processes in the detection of diabetic retinopathy. And also it
helps the ophthalmologists to detect the optic disc and the
vessels more easily and faster. Even on a poor computer
system, this technique can work effectively. This method can
work faster and it can process within a few minutes.
Therefore, this method is suitable for rural area in developing
countries.
6. CONCLUSIONS
Mathematical morphology method is used for optic disc and
the blood vessels detections. For these detections, the input
images are taken from the websites and "Eye and ENT
General Hospital (Mandalay). The input image is in RGB
colour space and for the further processes the image is
converted into appropriate colour space. The median filter,
averaging filter and the wiener filter are used for the noise
reduction. Among these filter, median filter is chosen for the
filtering purpose because median filter can reduce the effect of
noise without blurring the edge. And then, the adaptive
histogram equalisation technique is used for image
enhancement. It is also used to overcome the uneven
illumination case. Therefore, median filter and the adaptive
histogram equalisation techniques are used for noise reduction
and image enhancement purposes. Optic disc detection and the
blood vessels detection are the major role in the screening of
eye diseases. The results of this work can be used in the future
RGB to Gray
Median Filter
Contrast-limited adaptive Histogram
Equalization
histogram equalizationClosing
Filling
Thresholding
Blood Vessels
Detection

__________________________________________________________________________________________
processes such as the screening of diabetic retinopathy,
glaucoma and so on. This detection method doesn't need the
highly efficient computer so it is suitable for rural area in
developing countries.
ACKNOWLEDGEMENT
The author would like to thank to his supervisor Dr.Aung Soe
Khaing who gives the good advices for this research. The
author also would like to acknowledge the head of Department
of Electronic Engineering, Mandalay Technological
University. The author is highly grateful to all his teachers,
Department of Electronic Engineering, Mandalay
Technological University. And also the author would like to
thank to all doctors in “EYE and ENT General Hospital”
(Mandalay).
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BIOGRAPHIES
Oakar Phyo received his Bachelor degree in
Electronics from Technological University
(Mandalay), Myanmar in 2012. He is a master
candidate of Electronics Engineering
Department at Mandalay Technological
University. His interest research include image processing and
biomedical.
He received Bachelor of Engineering in
Electronics from Mandalay Technological
University, Mandalay, Myanmar, in 2004
and Master of Engineering in Electronics
from Yangon Technological University,
Yangon, Myanmar, in 2006. He has continued his PhD
dissertation in 2006. From October 2008 to September 2010,
he was doing research on Spatial Frequency Analysis of the
Human Brain at the Institute of Biomedical Engineering and
Informatics, Technical University Ilmenau, Germany. He

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received his PhD in Electronic Engineering from Mandalay
Technological University, Mandalay, Myanmar, in 2011.
He is now Associate Professor at Department of Electronic
Engineering, Mandalay Technological University, and
Mandalay, Myanmar. His research interests include computer
based Electrocardiogram (ECG) system, biomedical signal and
image processing, bioinstrumentation and telemedicine. Dr.
Aung Soe Khaing was responsible for the ECG laboratory for
the biomedical engineering students at the Institute of
Biomedical Engineering and Informatics, Technical
University Ilmenau, Germany from October 2008 to
September 2010.

Automatic detection of optic disc and blood vessels from retinal images using image processing techniques

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