National Instruments IMAQTM 用户手册

Contrast is the difference between the smallest and largest pixel values in a 
region. You can set the minimum contrast to potentially increase the speed 
of the pattern matching algorithm. The pattern matching algorithm ignores 
all image regions where contrast values fall beneath a set minimum contrast 
value. If the search image has high contrast but contains some low contrast 
regions, you can set a high minimum contrast value. Using a high minimum 
contrast value excludes all areas in the image with low contrast, 
significantly reducing the region in which the pattern matching algorithm 
must search. If the search image has low contrast throughout, set a low 
minimum contrast parameter to ensure that the pattern matching 
algorithm looks for the template in all regions of the image. Use 

CWIMAQMatchPatternOptions.MinimumContrast

 to set the 

minimum contrast.

If you know that the pattern rotation is restricted to a certain range, 
such as between –15

° to 15°, provide this restriction information to 

the pattern matching algorithm in the 

CWIMAQMatchPatternOptions.RotationAngleRanges

 property. 

This information improves your search time because the pattern 
matching algorithm looks for the pattern at fewer angles. Refer to 
Chapter 12, Pattern Matching, of the IMAQ Vision Concepts Manual 
for information about pattern matching.

To determine if the selected template or reference pattern is appropriate for 
the machine vision application, test the template on a few test images. 
These test images should reflect the images generated by the machine 
vision application during true operating conditions. If the pattern matching 
algorithm locates the reference pattern in all cases, you have selected a 
good template. Otherwise, refine the current template, or select a better 
template until both training and testing are successful.