PCA is a good technique to reduce the number of bands by first finding out the
correlation between various band combination which helps us remove the more correlated
bands such that we have less number of images carrying more information that makes
processing job easier.
Filters provide us a useful tool to focus some selected group of objects
with spatial frequency threshold. High pass filters emphasizes edges and provide more detail
of the images whereas low pass filter are very useful to get smoother images when we do not
need a very high detail of the images.