Sharp IV-S20 User Manual page 379

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Threshold value setting
The IV-S20 treats the "areas darker than the lower limit value" or "brighter than the upper limit value" as
"black." It treats that the areas between the upper limit value and lower limit value as "white." However, if
the white-black reverse function is enabled, conversion to white/black will be reversed. Normally, if you
want to use only one threshold value for binary conversion, set the upper limit value to "255." Then you
only need to adjust the lower limit value to a threshold value that works for our application.
(Captured image)
Binary conversion
(upper limit = A,
lower limit = B)
( Example for adjustment )
An example of adjustment is shown below, using a white object on a black background. When
the dotted line in the window is converted to a binary image, if the lower limit is set higher, the
black part in the binary image will become larger. If the lower limit is set lower, the white part
will become larger. Increase and decrease the lower limit value, find the value at which the
white part in the binary image starts growing and the value at which the black part starts
growing. Then set the lower limit at the value halfway between these points. This will ensure
reliable operation.
White
Inspection image
[W]
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Window
The IV-S20 captures images using CCDs, which are the light sensitive elements in the camera. The IV-
S20 may capture more than one target image to be measured for image processing, and it may capture
images not required for measurement. In these cases, a window is used to pick out just the desired target
for measurement. The area inside the window will contain the object to be measured and the areas
outside the window will be ignored.
Threshold value B
Binary conversion
(Upper limit = 255, lower limit = A)
Threshold value A
(Threshold value)
(Upper limit = 255, lower limit = A)
(Threshold value)
255
Upper
limit A
Lower
limit B
0
Black
255
White
0
Horizontal coordinate
of the dotted line
Changing the lower limit threshold value
* If the stable range in the lower limit threshold
value is less than 20, (actual measurement)
measurement errors may occur.
Window
G-11
Black
White
Black
The size of the white area changes
depending on the threshold value setting.
As the value increases,
the black part grows larger.
*
Stable range
As the value decreases,
the white part grows larger.
Object to be measured
Objects outside the designated
measurement area
Glossary
(Threshold value)
255
Lower White
limit A
Black
B
0
(Threshold value)
255
A
White
Lower
limit B
Black
0
G