Rockwell Automation 5370-CVIM2 Module - Manual (Page 450)

5 Chapter Chapter 8
Thresholds, Filters, and Morphology
8–11
Low threshold –– Any part of that image whose gray–scale brightness value
is lower than the low threshold value will appear white in the window. For
example, if the low threshold is 140, any part of the image whose brightness
value is lower than 140 will appear white in the window.
The interactive result of the two threshold settings is this: Any part of the
window image whose brightness value is between the high and low threshold
values will appear black in the window. (In the examples above, this would
apply to brightness values from 140 to 190.)
Dynamic Threshold Function
The dynamic threshold function can provide real–time threshold adjustments
to window tools and image tools that are configured for binary image
processing operations. This function involves using the results from a math
formula to adjust the high and/or low threshold values dynamically, during
run operations.
Specifically, when the “ High ” (or “ Low ”) box in the Thresh/Filter panel is
picked, as shown in Figure 8.8, a formula–entry keyboard appears, and the
appropriate formula can be entered at that point (by default, the current value
in the box will appear initially in the formula–entry field).
Figure 8.8 Example: Formula Entry Keyboard For Dynamic Threshold Function
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Figure 8.9 (page 8–12) illustrates using the dynamic threshold function to
maintain the “
Low ” threshold setting, under varying light conditions, for a
window tool that is configured to count pixels.