Rockwell Automation 5370-CVIM2 Module - Manual (Page 196)

5 Chapter Chapter 6
Reference Tools
6–37
This panel contains a pair of threshold adjustment cursors and two
morphology buttons,
and , which are used to create the
mask.
The cursors adjust the high and low masking thresholds, and the default
threshold settings are 255 and 128, respectively. The morphology buttons
access two stages of morphology operations, and the default morphology
selections are “MAX–MIN” for Morph 1 and “Identity” for Morph 2. If no
changes are made, these default settings will be used.
NOTE: The default morphology selections should not be altered except for
more advanced masking applications. For more information about
morphology functions, refer to Chapter 8, Thresholds, Filters, and
Morphology.
The combined effect of the default morphology settings is to identify areas of
high contrast. These “edge” areas are then used as a mask (and are shown in
green), and they are thus ignored during template matching operations.
During reference window operation, as the feature window searches for a
match in the search window, it ignores the masked pixels in the feature image
and uses only the non–green (that is, gray scale) pixels as the template.
The function of the threshold adjustments is to determine how strong an edge
pixel must be to be masked.
Figure 6.32 illustrates adjusting the masking threshold on the feature image
shown in Figure 6.30 (A). Note that when the
button is picked,
this image appears in the upper–left corner of the screen display
superimposed on the search window image, as illustrated earlier in
Figure 6.29 (page 6–34).
In Figure 6.32 (A), with the low threshold set to the default value of 128, the
mask (green areas) appears somewhat larger than required to cover the edge
pixels. When the low threshold is set to 160 (in this example), the mask is
reduced so that it covers only the edge pixels.
Figure 6.32 Threshold Adjustment to Optimize Masking Effect
Mask
(green areas)
Masking: low threshold = 160 Masking: low threshold = 128 A B