#1 How to use a filter image in GFourier?

[Anonymous]

I'd like to filter an artefact out of a CCD image. I
would do that by applying a mask image (all 1's with
some holes of 0's for data points that I want to
delete) to the FT's image.
I installed the Fourier plug-in, and tried to follow
the directions of thelast (5th) FAQ entry, which seems
to deal with just that. However, neither the frequency
image nor the inverse-transform result look like
what I would expect. I like to add that from the
description it is not always perfectly clear what
action from what menu you need to do in which
window.
So how exactly does the filter window work? It is not
documented (page linked in Instructions to
http://gfourier.sourceforge.net/filters.html
does not exist). In particular:
- What does the filter design stuff on top of the
filter window do?
- What do the axes mean, esp. the horizontal one?
- When applying a mask image, how is this influenced by
the graph on top?
Apparently it does have effect, but I don't
understand how to use it.

Please also e-mail me at tpeters@xs4all.nl

Thanx,