Image analysis – Applications – Document or print quality inspection
Reexamination Certificate
1999-04-05
2003-09-02
Mehta, Bhavesh M. (Department: 2625)
Image analysis
Applications
Document or print quality inspection
C382S141000, C382S111000, C356S237100, C250S559010
Reexamination Certificate
active
06614918
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light-and-shade inspection apparatus and method for use in inspection of light-and-shade defects on a plain material roll (or web) based on an image data which is produced by an image pick-up device picking up an image of the web (e.g., paper, film, nonwoven fabric, etc.) having a certain width and traveling in one direction. More particularly, the invention relates to a light-and-shade inspection apparatus for inspecting light-and-shade portions and a method for implementing it, by which variations of a background brightness (e.g., luminance) occurring in a width (e.g., transverse) direction of the web can be accurately eliminated.
2. Description of the Related Art
FIG. 10
is a block diagram showing a conventional light-and-shade inspection apparatus
1000
used for inspecting a web
2
. Apparatus
1000
includes a line-sensor camera
1
for picking up an image of the web
2
as an inspected object having a constant width and traveling in one direction, an illuminator
3
for illuminating a zone picked up by the camera
1
, and an image processing device
4
for processing data of an image picked up by the camera
1
and inspecting light and shade defects on the web.
The line-sensor camera
1
includes, for example, a photodetector array of 1024 elements (e.g., a charge-coupled device (CCD)) disposed along a line. Specifically, the camera
1
is disposed upwardly of a central portion of the web so that the photodetectors are arranged in a line array across the web in a transverse (width) direction thereof and in parallel with the transverse direction. The illuminator
3
is disposed downwardly of the web
2
(e.g., on the underside of the web), so as to illuminate the zone to be picked up by the camera
1
from a rear surface of the web
2
.
The image processing device
4
includes an image input portion
5
for performing an analog-to-digital (A/D)-conversion of a picked-up image signal outputted from the camera
1
and for capturing into the image processing device
4
the resultant (digitized) signal as an image data of luminance (e.g., lightness or brightness) information (e.g., specified with 256 levels of gray), a first comparator
6
coupled to an output of the image input portion
5
and adapted for comparing the image data with a first threshold value S
1
, and a second comparator
7
also coupled to the output of the image input portion
5
and adapted for comparing the image data with a second threshold value S
2
. The first threshold value S
1
is preset in a first preset device
8
and the second threshold value S
2
is preset in a second preset device
9
.
Referring to
FIG. 11
, an operation of the above-mentioned light-and-shade defect inspection apparatus
1000
will be described. In
FIG. 11
, a time-chart shows a lightness pattern of the image data obtained with one scan of the line-sensor camera
1
. In the time chart of
FIG. 11
, the horizontal axis (x) indicates a position on the web
2
in the transverse direction, whereas the vertical axis indicates a degree of lightness of the image data.
If the web
2
has thereon a defect which tends to increase a lightness (e.g., a hole or a flaw), there appears in the image data a high lightness portion (e.g., reference numeral
11
or
12
), as shown in FIG.
11
. The comparator
6
detects a light defect when this portion is higher than the first threshold value S
1
. On the other hand, if the web
2
has thereon a defect which tends to lower its lightness (e.g., caused by a stain, adhered foreign matter, etc.), there appears in the image data a low lightness portion (or a shade portion) indicated by numeral
13
or
14
, as shown in FIG.
11
. The comparator
7
detects a shade defect when this portion is lower than the second threshold value S
2
.
Thus, the conventional light-and-shade defect inspection apparatus
1000
inspects the presence or absence of light-and-shade defects by comparing the image data with two threshold values.
However, when the line-sensor camera
1
picks up an image of the web
2
while the web
2
is illuminated by the illuminator
3
as shown in
FIG. 10
, the lightness of the web
2
tends to increase at central and neighboring portions thereof due to characteristics of camera lenses and a condensing degree of the illuminator. As a result, the obtained image data of the picked-up image may vary, as shown in
FIG. 12
rather than that of FIG.
11
. In that case, if threshold values for the image data of
FIG. 12
are fixed as S
1
, S
2
shown in
FIG. 11
, defects such as numerals
11
A,
13
A of
FIG. 12
may not be detected, despite being detected correctly as true defects, since they are apparently smaller in magnitude or size than their corresponding threshold values.
In view of the foregoing, a light-and-shade defect inspection apparatus
1300
as shown in
FIG. 13
is known to eliminate the above-mentioned problem.
Referring to
FIG. 13
wherein like reference numerals of
FIG. 10
refer to similar parts, an image processing device
4
A is shown.
Image processing device
4
A includes an image input portion
5
for performing an A/D-conversion of a picked-up image signal outputted from the camera
1
and for capturing the resultant (digitized) signal as an image data into the image processing device
4
A, a one-dimensional filter
15
, coupled to an output of the image input portion
5
, for performing a smoothing processing of 1024 image data obtained by one scan of the camera
1
, a first adder
16
, coupled to an output of the filter
15
, for obtaining a first threshold value S
1
′ by adding a first preset value to a smoothed signal outputted from the filter
15
, and a second adder
17
, similarly coupled to the filter
15
, for obtaining a second threshold value S
2
′ by adding a second preset value to the smoothed signal.
Furthermore, the image processing device
4
A includes a first comparator
18
, coupled to outputs of the image input portion
5
and the first adder
16
, for comparing the image data with the first threshold value S
1
′, and a second comparator
19
, coupled to outputs of the image input portion
5
and the second adder
17
, for comparing the image data with the second threshold value S
2
′. Here, the first threshold value S
1
is preset in a first preset device
20
and the second threshold value S
2
is preset in a second preset device
21
.
With this configuration, the first and second preset values in the first and second preset devices
20
and
21
are respectively added to the smoothed signal obtained by the one-dimensional filter
15
, thereby allowing the respective preset values S
1
′ and S
2
′ to be changed in response to the web's lightness (luminance) variation across the width thereof. Hence, the defect
11
A and
13
A, which is not detected as defects in
FIG. 12
, can be detected as shown in FIG.
14
.
However, despite the improved apparatus, a problem associated with the known improved light-and-shade defect inspection apparatus
1300
resides in that an area of each defect shown in
FIG. 11
or
14
increases. It is noted that a length L of the defect appearing as an image data may be equal to or longer than an average length of data outputted from the one-dimensional filter
15
. In that case, a lightness variation due to the defect may be processed similarly to a lightness variation of the background lightness, and the threshold value will vary as the defect lightness. As a result, the calculation of the background lightness is affected by the defect lightness, thereby causing an error in a calculated value.
For example, a problem occur that only portions W
2
, W
3
could be detected as being defective within a zone W
1
which zone should be essentially detected as a defect but a central portion W
4
might not be detected as being defective.
The above problem is caused because an image pick-up range across the width of the web covered by the line-sensor camera is restricted, and the area of the defect
Carter Aaron
McGinn & Gibb PLLC
Mehta Bhavesh M.
Toshiba Engineering Corporation
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