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Fast regularity measures
for surface defect detection
Student
: Ming-Chun Chen
Advisor : Dr. Du-Ming Tsai
Department
of Industrial Engineering and Management
YUAN-ZE University
ABSTRACT
This research
proposes machine vision schemes for detecting subtle defects in non-textured
and homogeneously textured surfaces. The defects to be inspected are
ill-defined and hardly visible in the surfaces, which make the automatic
surface inspection task extremely difficult.
In this study,
regularity features of a small window sliding through the whole image are
extracted based on the consistence of spatial distribution of gray levels in
each window. Two methods are proposed. The first method is based on principal
component analysis (PCA) that calculates the eigenvalues
of the covariance matrix formed by the covariance of x- and y-coordinates
with the gray level as the weight. The smaller eigenvalue
λ2 is used as the
regularity feature, where a defective region will generate a feature value
smaller than that of a homogeneous defect-free region. The second method
divides the sliding window into a set of small non-overlapped blocks. The sum
of the gray levels in each block should be similar to each other if the
window of the sensed image contains no defects. The Chi-square ( χ2
) that measures the difference between the gray-level sum of a block
and the mean gray-level sum, and the entropy that measures the complexity of
the gray-level sums in all the blocks are then used as the regularity
measures. By using the integral image technique, the sum operations for all
three proposed regularity measures can be efficiently calculated for on-line,
real-time implementation.
The
experiments on a variety of textured and non-textured surfaces including
plastic case images of laptop computers, leather, TFT-LCD backlight panels
and backsides of solar wafers have shown the effectiveness of the proposed
methods. The computation times for an image of size 400×400 are only 0.032
seconds for λ2 and 0.28
seconds for χ2 and the
entropy measures on a typical personal computer.
Keywords: Machine vision; surface defect detection; texture analysis;
regularity
measure; principal component analysis; integral image
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《Demonstration》
【Plastic
case images of laptop computers】
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(a1)
Defective
image I
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(a2)
Detection
result of λ2
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(a3)
Detection
result of χ2
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(a4)
Detection result
of
Entropy
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(b1)
Defective
image II
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(b2)
Detection
result of λ2
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(b3)
Detection
result of χ2
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(b4)
Detection result
of
Entropy
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(c1)
Defect-free
image
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(c2)
Detection
result of λ2
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(c3)
Detection
result of χ2
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(c4)
Detection result
of
Entropy
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【Leather
A】
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(a1)
Defective
image I
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(a2)
Detection
result of λ2
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(a3)
Detection
result of χ2
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(a4)
Detection result
of
Entropy
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(b1)
Defective
image II
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(b2)
Detection
result of λ2
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(b3)
Detection result of χ2
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(b4)
Detection result
of
Entropy
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(c1)
Defect-free
image
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(c2)
Detection
result of λ2
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(c3)
Detection
result of χ2
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(c4)
Detection result
of
Entropy
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【Leather
B】
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(a1)
Defective
image I
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(a2)
Detection
result of λ2
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(a3)
Detection
result of χ2
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(a4)
Detection result
of
Entropy
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(b1)
Defect-free
image
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(b2)
Detection
result of λ2
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(b3)
Detection
result of χ2
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(b4)
Detection result
of
Entropy
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【Leather
C】
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(a1)
Defective
image I
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(a2)
Detection
result of λ2
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(a3)
Detection
result of χ2
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(a4)
Detection result
of
Entropy
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(b1)
Defective
image II
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(b2)
Detection
result of λ2
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(b3)
Detection
result of χ2
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(b4)
Detection result
of
Entropy
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(c1)
Defect-free
image
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(c2)
Detection
result of λ2
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(c3)
Detection
result of χ2
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(c4)
Detection result
of Entropy
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【TFT-LCD
backlight panels】
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(a1)
Defective
image I
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(a2)
Detection
result of λ2
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(a3)
Detection
result of χ2
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(a4)
Detection result
of
Entropy
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(b1)
Defect-free
image
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(b2)
Detection
result of λ2
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(b3)
Detection
result of χ2
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(b4)
Detection result
of
Entropy
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【Backsides
of solar wafers】
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(a1)
Defective
image I
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(a2)
Detection
result of λ2
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(a3)
Detection
result of χ2
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(a4)
Detection result
of
Entropy
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(b1)
Defective
image II
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(b2)
Detection
result of λ2
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(b3)
Detection
result of χ2
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(b4)
Detection result
of
Entropy
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(c1)
Defect-free
image
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(c2)
Detection
result of λ2
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(c3)
Detection
result of χ2
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(c4)
Detection result
of
Entropy
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