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Gaussian Pyramids

The Gaussian Pyramid is a hierarchy of low-pass filtered versions of the original image, such that successive levels correspond to lower frequencies.

  figure836
Figure 6.2: Gaussian pyramid

The low-pass filtering is done using convolution with a Gaussian filter kernel. Where the filter overhangs the image edges we reflect the image about its edge. Since the lowest frequencies have been removed, the full-size image contains redundant pixels. One may define the REDUCE operator which is a filtering followed by elimination of unnessesary pixels. For a filter kernel w[i,j] of dimension tex2html_wrap_inline2567 and reduction factor 4 we have:

equation842

There is a corresponding EXPAND operator which will reconstruct the low-pass filtered image by interpolating between pixels in the reduced image.

A Gaussian pyramid G(I) is defined on image I as:

eqnarray847



Jean-Michel JOLION
Tue Jun 20 08:41:17 METDST 2000