Panasonic IMAGECHECKER PV230 Manual page 23

Dynamic
It is helpful when the brightness of the background in the area is
uneven. For example, use it when the brightness of the left side and
the right side of the area is different like the example on the right.
Behavior of Dynamic Thresholding
1. Divide the inspection area by the specified size, and
calculate the average of the brightness in each divided
area.
In the right figure, the area where a letter "B" is located is
segmented into 4.
2. Extract pixels over "Average + Offset value" (when the
background is dark and characters are light) or pixels
below "Average - Offset value" (when the background is
light and characters are dark) as the pixels which comprise
characters in each area.
In case of the dark figure on the left, if the offset value has been
set to "15", the threshold of each area is calculated as follows
because the character is darker than the background.
- Threshold of lower left area: 110 - 15 = 95
- Threshold of upper left area: 120 - 15 = 105
- Threshold of upper right area: 130 - 15 = 115
- Threshold of lower left area: 125 - 15 = 110
3. Execute "2" in all the divided areas.
Calculating the average of the brightness in each inspection area
that has been divided makes extracting only the target characters
easier even when the thresholds for the brightness of the extracted
pixels differ in each area and the brightness is uneven.
Example)
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