To make fuller use of the additional
textural information in the IKONOS imagery, which has
around 25–50 pixels for each SPOT XS or Landsat TM
pixel, a 5 by 5 pixel variance filter was passed over each of
the three IKONOS depth-invariant bands (bands 1/2, bands
1/3, and bands 2/3) to create three textural layers for use in
supervised classification. To avoid creating artefacts around
edges of masked out areas such as land and clouds, the filter
was designed to ignore zero values