Image Acquisitionand Proces

Image Analysis 199
distance between them is trivial. For example, if a user draws a line ROI between
two points, the pixel distance between them can be easily determined (Figure 7.49
and Figure 7.50).
While this is simple when we know the spatial positions of the two points, it
becomes more difÞcult when their coordinates must be determined programmatically.
FIGURE 7.51 Finding edges and their parameters — wiring diagram.
7.7.3 FINDING EDGES PROGRAMMATICALLY
An edge in an image is generally deÞned as a feature interface with high contrast;
if an image’s intensity changes dramatically within a small spatial range, then it can
be considered as an edge. The IMAQ Edge Tool can be used to detect and classify
edges in an image by inspecting the pixel intensity values along a trace applied to
the image. The example in Figure 7.51 obtains the pixel coordinates of points along
a line ROI drawn by the user, and uses them to search for edges.
The pixel coordinates are obtained using IMAQ ROIProfile, and are wired into
IMAQ Edge Tool. IMAQ Edge Tool outputs the number of edges detected, their
coordinates and an array of clusters detailing comprehensive information regarding
each of the edges (Figure 7.52).
FIGURE 7.52 Finding edges and their parameters.
IMAQ Edge Tool is conÞgured by deÞning the edge parameters to use during
the search. Contrast speciÞes the threshold for the edge’s intensity difference
between features — edges with a contrast less than this threshold are not treated as
edges, and are subsequently ignored. The contrast is calculated as the difference