Image Processing Reference
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Fig. 3.3
Illustration of the hierarchical scheme for hyperspectral image fusion. (©2010 IEEE,
Ref: [88])
each of these subsets independently to obtain P fused images. Let us call them
first-stage fusion results. These P images form the base images (or inputs) for the
second-stage fusion. Now we may apply the same fusion algorithm over this image
cube of dimensions
. This procedure is repeated in a hierarchical manner
to generate the final result of fusion in a few stages. If we generate three such images
during the pre-final stage, and assign them to different color channels, we obtain the
RGB representation of the hyperspectral image.
Figure 3.3 shows the schematic of the hierarchical scheme of fusion. The scheme
begins with the formation of P subsets of hyperspectral bands each containing M
bands each, except the last one which may contain slightly less number of bands
depending upon the total number of bands K in the hyperspectral image. The first-
stage of fusion generates P intermediate fused images, one from each of the subsets
of the original data. The same process continues till the single fused image which
represents the combining of the entire data is generated. If the complete process
operates at J levels, at the pre-final stage, i.e., the ( J
1)-th stage, we obtain three
independent images each of them representing fusion of approximately one-third
dataset. We can create an RGB version of the fused image by assigning these three
images to red, green, and blue channels, respectively. The scheme brings flexibility
in terms of number of bands undergoing fusion. In literature, multi-resolution based
fusion techniques are sometimes referred to as the hierarchical fusion. The term
hierarchical has been used in a different context in this chapter. This scheme does
not perform any multi-resolution decomposition of the image/bands.
Typically, if we select M to be nearly 10% of the original number of bands K ,
then only those many bands are required to be present in the memory at any time. The
value of M , however, is subject to the choice of the observer, and does not much affect
the quality of the final result when the number of images being fused at any stage are
fairly equal. Although we have provided the illustrations by choosing the bands in
forward succession, the bands can also be combined in any randomorder for the given
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