filtering problem

[Dave Brennan <9147261b(at)clinmed.gla.ac.uk>]

Hi,

i don't know if anyone can help but it's worth a try!

I am trying to filter an array say (256x256) with a window of size 65x65
which scans across the array pixel by pixel. It should compare the
statistics of the area within the kernal with the global statistics of
the image to produce a correction image. (This is a particular type of
inhomogeneity correction)

In detail: 'the algorithm should correct the pixel value by a
multiplicative factor found by dividing the global mean by the window
mean'
A further problem is I want the ability to set a threshold where data
below the threshold are not included in the statistics and not corrected
by the algorithm.

At first I though I could just use convol to produce a correction map
but this does not allow me to set a threshold.

Does anyone have any ideas? It needs to be as fast as possible as it
will work on 128 images at a time.

Cheers

Dave Brennan