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Chapter 5
Performing Machine Vision Tasks
a.
b.
c.
d.
Figure 5-11. Selecting a Search Area for Grayscale Pattern Matching
Setting Matching Parameters and Tolerances
Every pattern matching algorithm makes assumptions about the images
and pattern matching parameters used in machine vision applications.
These assumptions work for a high percentage of the applications.
However, there may be applications in which the assumptions used in the
algorithm are not optimal. To efficiently select the best pattern matching
parameters for the application, you must have a clear understanding of the
application and the images you want to process. The following sections
discuss parameters that influence the NI Vision pattern matching
algorithm.
Match Mode
You can set the match mode to control how the pattern matching algorithm
handles the template at different orientations. If you expect the orientation
of valid matches to vary less than ±5° from the template, set
CWIMAQMatchPatternOptions.MatchMode to
cwimaqMatchShiftInvariant. Otherwise, set the mode element
to cwimaqMatchRotationInvariant.
Note
Shift-invariant matching is faster than rotation-invariant matching.
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NI Vision for Visual Basic User Manual