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The coarsest image computed crack pattern
in 5 cm meshes
computed items
Total length of crack : 210.64 cm
Density of crack : 842.56 cm/n*
Mean of crack width : 0.29 mm
Fig. 12. The coarsest image examined and its outcome
( sample No. 9 )
5. DISCUSSION
In the present examination 34 % of cracks
are undetected. It is realized that most
of undetected cracks are little contrast
to the concrete due to a certain stains
around them. The line-edge filter should
be more sensitive in such a condition
consequently. In order to make the filter
sensitive, thresholding in edge detecting
algorithm needs to be improved. In
particular a method of calculating
threshold value should be changed suit-
ably according to a condition around the
crack.
The measurement of crack width has been
accomplished with accuracy of the mean of
RMS error 0.08 mm, which is attained the
goal of this study intended. In order to
achieve more precise measurement of crack
width, it is needed that a resolution of
the original image should be more fine.
6 . CONCLUSION
To assess the deterioration of concrete
structures, an algorithm employed in a
prototype of crack measurement system
based on hierarchical image processing
technique has been examined with 18
samples of concrete crack images. The
algorithm .can be executed to detect and
measure the cracks ranging from 0.1 to
3.0 mm in width, in which a series of
images are generated and structured
hierarchically from fine to coarser, and
a single spatial filter is used for crack
detection.
As a result, 66 % of existing cracks on
the samples have been detected and meas-
urement of crack width has been performed
with an accuracy of 0.08 mm RMS. It is
clear that the edge detecting algorithm
should be improved to prevent from misde-
tection of cracks which are little con-
trast to concrete due to a certain
stains. The condition around cracks,
however, are changed so much in places
that no useful algorithm can be prepared
practically to apply to detecting every
crack influenced by every stain.
It is concluded that the algorithm exam-
ined in this study is useful to the crack
measurement system, although a improve-
ment of algorithm should be necessary to
eliminate such misdetection.
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Suzuki, H., Ito, S., Suzuki, A., Mori,
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