First the image cube was spatially filtered for every wavelength with an averaging filter with a structural element of
3×15 pixels, reflecting the difference in spatial resolution
in the x and y directions, to remove small irregularities such
as lenticels
In a second step the original
image cube was filtered again for every wavelength with an
averaging filter but now with a structural element of 64×320
pixels to provide a smooth background image without any
surface features