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For the fiducials like the ones shown in Figure 2(c)(d),
we use line intersection method to obtain sub-pixel accuracy. For the
shape as in Figure 2(c), the two short line segments in
the same direction are fitted into one line equation. The other two
line segments in the orthogonal direction are fitted into another line
equation. These two line equations are intersected to calculate the
center of the fiducial. The similar method can be used for the
fiducial shape as in Figure 2(d).
Our proposed algorithm for achieving the automated segmentation and
sub-pixel localization of fiducial marks is:
- Obtain sub images that contain the fiducial
marks near corners or edge-centers
from the original image.
- Select the colour band
that best represents the colour of the fiducial marks
if the images are colour images.
- Perform attribute-based morphology and other related processing
techniques to automatically
segment the fiducials as described in Section 2.3.
- Refine the positions of the fiducial marks obtained
from the previous step by using the Optimum Location or
Line Intersection method.
Mon Dec 8 15:45:35 EST 1997