EN
84
Software Module
Construction
Method
Edge on Line
First of all, the search line’s gray-scale values are determined. Then a derivative is
generated from the gray-scale values in order to ascertain where an edge is located. If
several edges are found, polarity and the “find by” specification determine which edge
will be used as a point for the coordinate system.
Example: The first transition from dark to bright should be detected as an edge in the
following image.
The search line’s gray-scale values are represented in the profile.
The search line’s gray-scale values are represented in the profile.
The profile’s derivatives are shown in this diagram for edge widths of both 3 and 9.
If the positive threshold gradient is 150 and the negative threshold gradient is -120,
edges are detected close to the pixels 16, 18 and 24 (if an edge width of 3 has been
selected), because the derivative exceeds the positive threshold gradient and or lies
below the negative threshold gradient at these points. In contrast, no edges would be
detected with an edge width of 9.
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