The DE_SPIKER function returns a cleaned image by removing spikes at a
specified input level. The technique used is to difference a smoothed image
and the input image and find all pixels that deviate
by more than a given threshold.
IDL> clean_img = de_spiker(image, thresh)
IDL> clean_img = de_spiker(image, thresh, /neg)
IDL> clean_img = de_spiker(image, thresh, indices=indices)
where, image is the input data array, thresh is the specified spike amplitude to
remove. Optional input/output parameter indices contains the indices of
spikes at the level specified, and optional input switch /neg requests that
``dark holes'' be removed.