An Efficient Algorithm for Edge Detection of Corroded Surface

Karamjeet Singh Virk Int. Journal of Engineering Research and Applications www.ijera.com
ISSN : 2248-9622, Vol. 5, Issue 6, ( Part -1) June 2015, pp.91-96
www.ijera.com 91 | P a g e
An Efficient Algorithm for Edge Detection of Corroded Surface
Karamjeet Singh Virk*, Dr. Sukhjeet K. Ranade**
*(Department of Computer Science, Punjabi University, Patiala)
** (Department of Computer Science, Punjabi University, Patiala)
ABSTRACT
Inspection process in industrial applications plays a vital role as it directly hinders the outages of industry.
Thereby the inspection especially in case of corroded surfaces is to be fast, precised and accurate. Visual
inspection has been very liable to mistakes because of numerous facts. The automatic inspection systems remove
subjective aspects and can provide fast and accurate inspection. Inspection of corroded surfaces is very important
concern, thus it is required to detect corroded surfaces. A new algorithm is developed by certain changes in mask
and thresholding selection to detect corroded surfaces. The paper is about how we can amend the weak edges of
input images and discarding false edges to overcome the problem of traditional techniques in this field. Proposed
operator also compared with two commonly used edge detection algorithms which are Canny and Sobel.
Keywords - Canny edge detector, Corroded Surfaces, Edges, Proposed modified edge detector, Sobel edge
detector
I. INTRODUCTION
Edge detection is a procedure that perceives the
existence and position of edges established by sharp
variations in brightness or colour intensity of an
image. Subsequently, it can be verified that the
incoherence in surface alignment, variations in
properties of material and deviations in scene
brightness. In the idyllic situation, the outcomes of
implementing an edge detector to an image may
results into a set of associated curves that specifies
the outlines of an object, the outlines of surface
design also curves that resembles to incoherence in
surface alignment.
In industry, technical and scientific advances in
computer technologies, digital image processing,
image pattern recognition and artificial intelligence
made industrial image analysis easier and effective.
Visual inspection applications are present in
industries that include visual quality control. In
particularly, the main point of our interest is corroded
surfaces in industry and visual inspection of that.
Visual control has been usually performed by human
vision: corroded surfaces have been inspected by
workers that verify the quality and age of that. This
way of inspected has been very liable to mistakes. So,
there was a large influence of human errors and
subjectivity on the result of inspection. The automatic
inspection systems remove subjective aspects and can
provide fast and accurate inspection. These
inspection systems are based on image processing so
the so many edge detection techniques are present.
In all edge detection algorithms, the main
objective is to locate the edge from the scene neither
with prior information nor with human interpretation.
Some popular algorithms include Sobel, Roberts,
Prewitt, LOG and Canny Algorithm. These edge
detection operators share almost the same concept
which is to find the abrupt change in intensity level
and locate true and false edges accurately. Canny
edge detector has proven to be superior over many of
the available edge detection algorithms and thus was
chosen mostly for real time implementation and
testing.
Canny edge detector is not simply a noise
disturbed and makes an even trade-off between noise
and edge detection of an image. Canny edge detector
has precise edge detection but quite sensitive to noise
and find the accurate weak edges. A pixel position is
professed by an edge position, if gradient magnitude
surpasses some threshold, an edge can be detected for
every value that surpasses the threshold. The above
mentioned issue is of a great importance in noisy
images or industrial application where many false
edges resulting from noise are detected.
In this paper, a new Proposed modified edge
detection algorithm has been developed and is
applied to various applications of the industry to
detect the corroded surfaces. In this paper we studied
the various techniques of image edge detection firstly
and come to know how to detect the corroded
surfaces and then used various morphological
operations like dilation followed by hole filling and
at last used erosion and then computed true and false
edges of corroded surfaces. Corrosion detection is
very important part of industrial inspection process
and this paper represents it. This paper is organized
into various sections which are as follows:
Background of approach is described in Section 2.
The proposed modified edge detection algorithm is
described in Section 3. Results are drowned and
discussed in Section 4. Finally, conclusions and
future scope are drawn in Section 5.
RESEARCH ARTICLE OPEN ACCESS

II. BACKGROUND
This method was presented by John F. Canny in
1986. Even though this method is quite old but is still
used because of its precision in image edge detection.
Canny edge detector is not simply a noise disturbed
and makes an even trade-off between noise and edge
detection of an image. It can also find the weak edges
accurately. A pixel position is professed by an edge
position, if gradient magnitude surpasses some
threshold, an edge can be detected for every value
that surpasses the threshold. Typical implementation
of the Canny edge detector as follows:
2.1 Noise reduction by smoothing:
Noise contained image is smoothed by
convolving the image I(i, j) with Gaussian filter G.
Mathematically, the resultant smoothing image is
given by:
(i, j) G*I(i, j)F  (1)
2.2 Finding gradients:
In this step we detect the edges where the change
in grey scale intensity is at maximum level. Gradient
of an image helps us to determine the required areas.
Usually, canny operator is used to determine the
gradient at each pixel of a smoothed image. Canny
operators in i and j directions are given below:
1 0 1
2 0 2
1 0 1
iD
  
 
   
   
,
1 2 1
0 0 0
1 2 1
jD
   
 
  
     (2)
These Canny masks are convolved with smoothed
image and gives gradients in i and j directions:
*F(i, j)i iG D , *F(i, j)j jG D
(3)
Therefore magnitude of gradient of a pixel of input
image is given by:
2 2
i jG G G 
(4)
The direction of gradient is given by:
arctan j
i
G
G

 
  
 
(5)
iG and jG are the gradients given in the i and j
directions respectively.
2.3 Non maximum suppressions:
Non maximum suppression is carried out to
preserves all local maxima in gradient image, and
discarding everything else, the result is presented in
thin edges.
• Firstly round the gradient direction  nearly 45°,
then compare the gradient magnitude of the pixels in
positive and negative gradient directions i.e. if the
gradient direction is in east then compare gradient of
the pixel with the west direction say E (i, j) and W (i,
j) respectively.
• If the edge strength of image pixel is larger than that
of E (i, j) and W (i, j), then preserves the value of
gradient and mark as edge pixel, if not then
suppressed.
2.4 Hysteresis thresholding:
The output of non-maxima suppression still
contains the local maxima created by noise in image.
Instead of choosing a single threshold value, we use
two thresholds values to overcome the problem of
streaking i.e. hight and lowt are used.
The Sobel edge detection is commonly used
method edge detection The Sobel edge detection
technique is presented by Sobel in the year 1970. The
Sobel technique of edge detection is based on image
segmentation detects edges by Sobel estimation to the
derivative value. It points the edges to individual
points wherever the gradient is high. The Sobel
operator consists of a pair of 3×3 convolution kernels
as revealed in Table 3.1. One kernel is just replica of
other by rotating it by 90°.
Table 1. Sobel operator mask.
-1 -2 -1 +1 0 -1
0 0 0 +2 0 -2
+1 +2 +1 +1 0 -1
These kernels are intended to reply extremely
to edges run horizontally and vertically
comparative to pixel grid, one kernel for both two
perpendicular alignments. The kernels can yield
distinct quantities of the gradient component for
each alignment (Gx and Gy).
III. PROPOSED MODIFIED EDGE
DETECTION ALGORITHM
The proposed modified operator draw attentions
to the regions of high spatial frequency correspond to
the edges of the image and also perform the 2-D
spatial gradient quantity. Edges are running
diagonally corresponding to the horizontally and
vertically relative to the pixel, which get maximum
responds from the two designed kernels and one
kernel is for each orientation. The Proposed modified
edge detector algorithm intended by using a new
mask motivated by the mask of Sobel edge detector
and by assortment of suitable threshold value that
adapts itself according to the needs of an the
application.
The proposed modified edge detector consists of
3×3 pair of matrix of convolution kernels as shown in
Table 2. These values are taken from traditional

operator; however, these are rotated diagonally over
the axis to make the new mask. Similar to Canny
filter and Sobel filter, the new masks generated also
has zero value in central rows and columns of the
mask. Now, the above kernels are used to generate
the separate gradient components (Gx and Gy) in
each orientation by applying the kernels to the image,
which is as follows:
Gx=(f(i,j-2)+f(i,j-1)+f(i,j))-(f(i-2,j-2)+f(i-2,j-1)
+f(i-2,j)) (6)
Gy=(f(i-2,j)+f(i-1,j)+f(i,j))-(f(i-2,j-2)+f(i-1,j-2)+
f(i,j-2)) (7)
Now Gx and Gy are combined and gives the
result of absolute magnitude of gradient at each point
which is presented below in the form of equation:
|G|= Gx2+Gy2 (8)
Table 2. Masks used by the Proposed modified
operator.
-1 -2 -1 +1 0 -1
0 0 0 +2 0 -2
+1 +2 +1 +1 0 -1
Gx Gy
Table 3. Selection of pixels by the Proposed modified
operator.
i-2,j i,j i-2,j i-1,j i,j
i-2,j-1 i,j-1
i-2,j-2 i,j-2 i-2,j-2 i-1,j-2 i,j-2
Gx Gy
Sobel and Canny edge detectors are used
to apply on established industrial application.
Whereas proposed modified algorithm is efficient
to adapt itself according to the needs of the
industrial applications. In this manner, an outcome
of proposed modified algorithm seems to be more
accurate and precised in case of industrial
requirements when compared with Sobel and
Canny algorithms.
IV. RESULTS AND DISCUSSION
This section presents the results of the Proposed
modified filter in comparison to the Sobel and Canny
edge detection methods. These edge detection
techniques were implemented using Matlab 2012,
and tested for many practical images.
4.1 Original Image 1
(a) Original image 1
(b) Sobel Operator
(c) Canny operator
(d) Proposed modified operator
figure 1. (a) original image 1, (b) sobel operator, (c)
canny operator and (d) proposed modified operator

(b) Sobel operator
(c) Canny operator
canny operator and (d) proposed modified operator
(b) Sobel operator
(c) Canny operator
canny operator and (d) Proposed modified operator

4.4 Comparative study
Table 4. Comparative study of Original Image 1
Image Total
pixel
(T)
Accepte
d pixel
(A)
Rejected
pixel (R)
Accurac
y (%)
Original
image 1
(Grey)
50325 3662 46663 100
Sobel
inverted
segmented
image
50325 2082 48243 56.8
Canny
inverted
segmented
image
50325 4395 45930 80
Proposed
inverted
segmented
image
51245 3343 47902 91.2
Table 5. Comparative study of Original Image 2
Image Total
pixel
(T)
Accepted
pixel (A)
Rejecte
d pixel
(R)
Accur
acy
(%)
Original
image 2
(Grey)
220675 35337 185338 100
Sobel
inverted
segmented
image
220675 8996 211679 25.4
Canny
inverted
segmented
image
220675 60092 160583 30
Proposed
inverted
segmented
image
222559 37505 185054 93.9
Table 6. Comparative study of Original image 3
Image Total
pixel (T)
Accepted
pixel (A)
Rejected
pixel (R)
Accuracy
(%)
Original
image 3
(Grey)
140125 25864 114261 100
Sobel
inverted
segmente
d image
140125 4978 135147 19.2
Canny
inverted
segmente
d image
140125 37815 102310 53.8
Proposed
inverted
segmente
d image
141669 27008 114661 95.6
V. CONCLUSION AND FUTURE SCOPE
From the above study, we concluded the
proposed modified edge detector is very effective for
edge detection purposes. It is observed that for the
four images used, there are less false edges in the
proposed modified edge detector. From the results, it
is concluded that results obtained from the modify
detector shows that it detect less false edges and also
improve intensity level of edges as compared to
Sobel and Canny edge detector. Edge detection is the
foremost field of inspection in modern industry in
now a day. Canny detector is universally accepted
technique but it is not suited all the way as it fails to
give accurate performance in certain areas. It detects
large number of weak edges also. Application of the
corroded surfaces detection is one in which canny
and sobel detector are not ideally performed. Thus, to
overcome such type of problems a new edge detector
is developed and outcome of this detector reflects its
performance.
The work can be improved in the future by using
the same mask with image sharpening filters. For
example, we can use median filtering to improve the
method. Noisy contents are removed from the image
by using the above filter. In some cases the noisy
contents are taken as false edges. So the median filter
can be used as a preprocessing step prior to image
sharpening and can help to take out unwanted
components present within an image. The improved
filter can also further implemented on different type
of applications. In the case of critical and complex
application, evolutionary algorithms may evolve with
this design. This can further improve the filter in the
terms of performance.
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An Efficient Algorithm for Edge Detection of Corroded Surface

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