National Instruments IMAQ Vision for LabWindows TM /CVI - Manual (Page 74)

Chapter 5 Performing Machine Vision Tasks
IMAQ Vision for LabWindows/CVI User Manual 5-22 ni.com
Defining a Search Area
Two equally important factors define the success of a color pattern
matching algorithm—accuracy and speed. You can define a search area to
reduce ambiguity in the search process. For example, if your image has
multiple instances of a pattern and only one instance is required for the
inspection task, the presence of additional instances of the pattern can
produce incorrect results. To avoid this, reduce the search area so that only
the desired pattern lies within the search area. For example, in the fuse box
inspection example, use the location of the fuses to be inspected to define
the search area. Because the inspected fuse box may not be in the exact
location or have the same orientation in the image as the previous one,
the search area you define must be large enough to accommodate these
variations in the position of the box. Figure 5-12 shows how you can select
search areas for different objects.
Figure 5-12. Selecting a Search Area for Color Pattern Matching
1 Search Area for 20 Amp Fuses 2 Search Area for 25 Amp Fuses
1 2