National Instruments IMAQTM - Manual (Page 77)

Chapter 5 Performing Machine Vision Tasks
© National Instruments Corporation 5-25 IMAQ Vision for Visual Basic User Manual
Minimum Contrast
Use the minimum contrast to increase the speed of the color pattern
matching algorithm. The color pattern matching algorithm ignores
all image regions where grayscale contrast values fall
beneath a set minimum contrast value. Use
CWIMAQMatchColorPatternMatchingOptions.MinimumContrast
to set the minimum contrast. Refer to the Setting Matching Parameters and
Tolerances section of this chapter for more information about minimum
contrast.
Rotation Angle Ranges
If you know that the pattern rotation is restricted to a certain range, provide
this restriction information to the pattern matching algorithm by using
the
CWIMAQMatchPatternOptions.RotationAngleRanges property.
This information improves the search time because the color pattern
matching algorithm looks for the pattern at fewer angles. Refer to
Chapter 12, Pattern Matching, in the IMAQ Vision Concepts Manual
for more information about pattern matching.
Testing the Search Algorithm on Test Images
To determine if the selected template or reference pattern is appropriate for
the machine vision application, test the template on a few test images by
using the
CWIMAQVision.MatchColorPattern method. These test
images should reflect the images generated by the machine vision
application during true operating conditions. If the color 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.
Finding Points Using Color Location
Color location algorithms provide a quick way to locate regions in an image
with specific colors.
Use color location under the following circumstances:
• Requires the location and the number of regions in an image with their
specific color information
• Relies on the cumulative color information in the region, instead of the
color arrangement in the region
• Does not require the orientation of the region