National Instruments IMAQTM - Manual (Page 65)

Chapter 5 Performing Machine Vision Tasks
© National Instruments Corporation 5-13 IMAQ Vision for Visual Basic User Manual
3. Define an image or an area of an image as the search area. A small
search area reduces the time to find the features.
4. Set the tolerances and parameters to specify how the algorithm
operates at run time using CWIMAQMatchPatternOptions.
5. Test the search algorithm on test images using
CWIMAQVision.MatchPattern2 .
6. Verify the results using a ranking method.
Defining and Creating Effective Template Images
The selection of a effective template image plays a critical part in obtaining
good results. Because the template image represents the pattern that you
want to find, make sure that all the important and unique characteristics of
the pattern are well defined in the image.
Several factors are critical in creating a template image. These critical
factors include symmetry, feature detail, positional information, and
background information.
Symmetry
A rotationally symmetric template is less sensitive to changes in rotation
than one that is rotationally asymmetric. A rotationally symmetric template
provides good positioning information but no orientation information.
Figure 5-7. Symmetry
a Rotationally Symmetric b Rotationally Asymmetric
a. b.