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9.3. Mosaicing and Making Panoramic Images 229
Of course, getting the iterative algorithm started is no easy matter. When
building a panorama, it is likely that image I
n
will have a lot of overlap with
I
n−1
, and so starting with the R that placed I
n−1
in the panorama is probably
the best way to generate an initial guess. However, if the overlap between two
successive frames is small (less than 50%), an alternative strategy of determin-
ing R, or at least getting an initial guess for it, must be followed. The two
most successful appr oaches are:
1. Hierarchical matching. Small subsampled and smoothed versions of I
n
and I
c
are made, e.g., images may be downsampled from 512 ×512 to
32 × 32 as a first guess. In these smaller images, the overlap appears ...