National Instruments IMAQ Vision for LabWindows TM /CVI - Manual (Page 38)

Chapter 3 Making Grayscale and Color Measurements
© National Instruments Corporation 3-9 IMAQ Vision for LabWindows/CVI User Manual
Comparing Colors
You can use the color matching capability of IMAQ Vision to compare or
evaluate the color content of an image or regions in an image.
Complete the following steps to compare colors using color matching:
1. Select an image containing the color information that you want to use
as a reference. The color information can consist of a single color or
multiple dissimilar colors, such as red and blue.
2. Use the entire image or regions in the image to learn the color
information using
imaqLearnColor() , which outputs a color
spectrum that contains a compact description of the color information
in an image or ROI. Use the color spectrum to represent the learned
color information for all subsequent matching operations.
Refer to Chapter 14, Color Inspection, of the IMAQ Vision Concepts
Manual for more information about color learning.
3. Define an entire image, a region, or multiple regions in an image as the
inspection or comparison area.
4. Use imaqMatchColor() to compare the learned color information to
the color information in the inspection regions. This function returns
an array of scores that indicates how close the matches are to the
learned color information.
5. Use the color matching score as a measure of similarity between the
reference color information and the color information in the image
regions being compared.
Learning Color Information
Choose the color information carefully when learning color information.
• Specify an image or regions in an image that contain the color or color
information that you want to learn.
• Select the level of detail you want the for the learned color information.
• Choose colors that you want to ignore during matching.
Specifying the Color Information to Learn
Because color matching only uses color information to measure similarity,
the image or regions in the image representing the object must contain only
the significant colors that represent the object, as shown in Figure 3-6a.
Figure 3-6b illustrates an unacceptable region containing background
colors.