STANDARD DEVIATON

[Ben Marriage <ben(at)met.ed.ac.uk>]

Hi all,

I want to calculate the standard deviation of a 3x3 pixel area for each
element of a satellite image (5000x2000 pixels). At the moment I use for
loops to scan through the image and then use the built-in IDL standard
deviation routines. I've tried to speed this up with the use of
convolution and whatnot but never seemed to solve the problem. Does
anyone know of a simple and elegant (read "quick") method of doing this
without using loops?

Thanks,
Ben Marriage
Department of Meteorology, University of Edinburgh