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Application of frequency domain processing
to X-ray radiographic images of welding

quality of X-ray images is frequently sensitive for noise, lighting and working place surroundings. Therefore, such images
need to be carefully examined to identify welding discontinuities. However, the human interpretative are usually contradictory
and may cause confusion. Present work has proposedan image processing technique based on frequency domain processing to
clarify the X-ray radiographic images taken for different welding discontinuities. The images are captured using low-resolution
video camera and high-resolution digital camera. Preprocessing imaging tasks are performed to reduce the noise in the lowresolution
video sequence images. Subsequently, low-pass followed by emphasishigh-pass frequency filters are applied to
enhance the images with appropriate cut-off frequencies. It is found that high-frequency domain image filtering is enhancing
the morphological features of the X-ray images. The enhanced images become visually cleared and the welding discontinuities
are possibility accessible.
Keywords: Welding discontinuities, frequency domain analysis, imagefiltering, image enhancement, nondestructive testing,
X-ray film
1. Introduction
It is a matter of fact that neither construction materials nor engineered structures are free from imperfections
[1]. Fusion welding joints are not exceptions and always contain randomly discontinuities, which
are interruptions in the desirable physical structure of a weld. These discontinuities may be attributed
tofour broad reasons: design, welding process, metallurgical and nonqualified welders related. It is
also possible to classify welding discontinuities into main six categories [2]: undercut; slag inclusions;
porosities; lack of fusion; lack of penetration and cracks. According to the amounts and the dimensions
of such discontinuities, the acceptance or the rejection decision of the welding jointswill be taken. If it
∗Corresponding author. E-mail:
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148 M.I. Rajab et al. / Application of frequency domain processing to X-ray radiographic images of welding defects
Frequency Domain
Noise reduction
Image resizing & converting
into gray scale intensity
Highpassemphasis filtering
X-ray films of the welding
Digital image capturing
Fig. 1. Steps of the used image processing.
is dangerous to use welding joints that have specific amounts and dimensions of certain discontinuities
in an application, such discontinuities will be considered as defects. By definition, a defect is a condition
that must be removed or corrected. Most ofwelding joints discontinuities cannot be removed or even
corrected, simply the defected welding joints must be welded again, which mean much cost and effort
will be lost. Therefore, either acceptance or rejection decision must be accurately taken.
Different methods [1] are used for thorough inspection of the welding joints in order to define
location, size, orientation and structural significance ofthe welding discontinuities. Nondestructive
testing evaluation (NDT) comprises a range of test methods for detecting discontinuities in a welding joint
without causing damage. One of the most NDT techniques used for inspecting several types of welded
assemblies is radiographic testing. ASM handbook [1] has considered radiographic testing technique
as most suitable technique used for almostall materials, all weld geometries and main discontinuities
categories. The radiographic testing technique uses radiation, either as X-rays or gamma rays, to penetrate
the weld to create a latent image on radiographic positive film. The test piece absorbs radiation, but when
flaws are present, less is absorbed than the amount absorbed by the parent material, which produces
a localized...
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