Posted by
Divakar Ramachandran-2 on
Nov 10, 2013; 3:34am
URL: http://imagej.273.s1.nabble.com/Band-pass-filter-tp5005522.html
Hello,
This is about the band-pass filter option available under Process - FFT.
I work primarily with lattice images. The power spectrum displayed using
Process - FFT has peaks corresponding to the periodicity of lattice
fringes in my image. The band-pass filter could be an option in some of
the cases to filter out non-periodic noise. However, I have been unable
to understand the input values for the band-pass dialog box. The
documentation says about the 'filter large structures down to' and
'filter small structures up to' fields the following "Note that these
values are both half the spatial frequencies of the actual cutoff" This
is unclear to me - are these values in pixel units, or scaled units, and
are they to be given in real space units or in the spatial frequency
domain? The default values of 40 and 3 seem to work for many of my
images though. Looking at the mask created, these numbers do not seem to
match the spatial frequencies seen in the power spectrum of the image
displayed with Process -> FFT -> FFT. In fact the mask seem to be in
real space and is not treated as a Fourier space object - x, y are
displayed in pixel units in the status bar of the main ImageJ window.
So, how is this mask applied to the image?
Any pointers to a better understanding is most appreciated.
Thanks,
Divakar
--
*Dr Divakar Ramachandran* Anupuram, TN 603127, India
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