FFT-Filtering - are non-symmetric masks useful?

Posted by Michael Schmid on Dec 11, 2007; 7:42pm
URL: http://imagej.273.s1.nabble.com/FFT-Filtering-are-non-symmetric-masks-useful-tp3697755.html

Hi FFT experts,

for filtering images in the Fourier domain, one can paint white
or black on the power spectrum shown after Process>FFT (to pass
and remove the selected areas when transforming back).

The power spectrum has inversion symmetry.
Currently, one has to paint two areas for all off-center
positions, because they appear twice in the power spectrum.
For an example, see the two black bars in the bottom left
image in
   http://rsb.info.nih.gov/ij/docs/examples/FFT/

My question to the FFT experts: Is there any useful application
of filtering only on one side of the center?

Otherwise, with a small modification to the ImageJ code I could
avoid extra work by painting on one side only, having ImageJ do
the other side.
(Sometimes I have to filter or block many spatial frequencies,
then painting them twice makes a difference).

Michael