Rockwell Automation 5370-CVIM2 Module - Manual (Page 441)

Chapter 8
Thresholds, Filters, and Morphology
8–2
Settings can be changed by “dragging” the cursors up and down, or by
picking the screen above or below a cursor. Alternatively, the settings can be
changed by picking the box containing the current value and entering a
specific value on the calculator pad, for gaging tools, or on a formula–entry
keyboard for area tools using binary thresholding. In the latter case, the
keyboard can be used to enter either a constant, for static thresholding, or a
math formula, for dynamic thresholding (refer to the Dynamic Threshold
Function section on page 8–11 of this chapter for details).
Your main objective in setting the binary threshold is to define the most
stable edges along the gage where the gage crosses the proposed reference
points on the workpiece image.
The binary threshold setting affects only the part of the workpiece image
lying within a small box that surrounds the gage. Within that box, the
workpiece image is binarized –– that is, its features appear as either black or
white. The reason for displaying the binarized image is to provide a visual
aid for setting the binary threshold.
Threshold Settings: Left and Right Cursors
The two thresholds interact to affect the appearance of the binarized
workpiece image within the binarized image box. Individually, the two
threshold settings have the following effects:
•
High threshold (left cursor) –– This setting determines the high
threshold value for the binarized image. Any part of that image whose
original gray–scale brightness value is higher than the high threshold
value will appear black in the binarized image.
For example, if the high threshold setting is 190, any part of the binarized
image whose brightness value is higher than 190 will appear black.
•
Low threshold (right cursor) –– This setting determines the low
threshold value for the binarized image. Any part of that image whose
original gray–scale brightness value is lower than the low threshold value
will appear black in the binarized image.
For example, if the low threshold setting is 40, any part of the image
whose brightness value is lower than 40 will appear black.
The interactive result of the two threshold settings is this: Any part of the
image (in the binarized image box) whose original brightness value is
between the high and low threshold values will appear white in the box. (In
the examples above, this applies to brightness values from 40 to 190.)
Figure 8.2 (page 8–3) illustrates a binarized image with optimized
thresholds.
Gaging Tools: Binary
Threshold Procedures