Image Acquisitionand Proces

Image Processing 89
FIGURE 5.7 Oval ROI deÞnition.
5.1.2.1 Rotated Rectangle
As its name would suggest, rotated rectangles are similar to their simple counterparts,
but with the added functionality of allowing the user to rotate them. When a rotated
square or rectangle is deÞned, several extra construction lines are evident (Figure 5.8).
The masked rotated rectangle ROI in Figure 5.8 was achieved with the code
shown in Figure 5.9.
5.1.2.2 Annulus Arc
An annulus is deÞned as the Þgure bounded by and containing the area between
two concentric circles and an annulus arc is, as you might expect, an arc component
of that annulus (Figure 5.10).
An annulus arc is very useful when unwrapping text, or any otherwise wrapped
image data, for analysis. DeÞning an annulus arc takes place in four steps, as shown
in Figure 5.11(a) deÞning the outer radius, Figure 5.11(b) the starting edge, Figure
5.11(c) the ending edge and Figure 5.11(d) the inner radius.
Using the Annulus Arc selection tool alone may seem of little or no use, if it is
combined with an unwrapping routine (IMAQ Unwrap, for example) you can unwrap
a semicircular portion of an image, distorting it to a rectangular shape, as shown in
Figure 5.12. This example waits for a Draw Event on either of the IMAQ windows
and once one is detected, that window’s ROI is returned, converted from a raw ROI
to an annulus arc and then IMAQ Unwrap is called to unwrap the annulus arc into a
rectangle.
The unwrapped image (the ßoating window containing the text in Figure 5.13)
can then be fed through optical character recognition (OCR) software, including the