Panasonic PV500 User Manual page 136

Using Subtraction Function
Subtraction function extracts a pixel that exceeds a certain degree of the difference in the gray value comparing
the detected area and the template. With this feature, the PV can detect up to 128 subtraction parts that are
difficult to reflect in the correlation value. It judges the object based on the number of detected subtraction
parts.
Items Related to Subtraction
Subtraction Threshold
The checker extracts pixels that exceed the set degree of the difference in the grayscale value or more
between the detected image and the template. The lower the Subtraction Threshold value, the stricter
extraction standard is.
Filter
Dilates or erodes the pixel clusters extracted under the condition of Subtraction Threshold value, or does
so after dilation or erosion. Use the Filter function to enhance the extracted pixel cluster or remove fine
noises or dusts.
Min. Subtracted Size
The checker detects only the clusters of the filtered extraction pixels having the area value more than the
Min. Subtracted Size. For example, not to detect 10-pixel or less of extracted subtraction parts, set Min.
Subtracted Size to "11".
Max. OK No. of Subtracted Objects (0-128)
A tolerance of a detected pixel cluster. If the number of detected pixel clusters is less than the Max. OK No.
of Subtracted Objects, the object will be judged as "OK".
1.
Select "Subtraction".
2.
Select "Yes" for "Subtraction".
3.
Enter the values in "Min. Subtracted Size" and
"Subtraction Threshold".
4.
Select "Filter".
No (Default)
3x3 (5x5) Erosion: Deletes fine noises.
3x3 (5x5) Erosion -> Dilation: After deleting noises, restore the left parts to the original size.
3x3 (5x5) Dilation -> Erosion: Filter processing to fill holes within the detect area.
5.
Enter the values in "Max. OK No. of Subtracted Objects".
Specify tolerance of the number of extracted parts as the result of subtraction. When performing
subtraction, this judgement is a judgement of checker.
When the result of No. of Objects exceeds 128, it becomes "255" automatically and the object is judged as
NG.
6.
After the setting is completed, press the CANCEL key.
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