Low- and high-pass filter

Posted by Vincent Wolowski on Nov 25, 2013; 1:02pm
URL: http://imagej.273.s1.nabble.com/Low-and-high-pass-filter-tp5005690.html

Dear all,

I am trying to understand how to use the Process/FFT/Bandpass Filter
for low- and high-pass filter on 16-bit images. I have read the
documentation here: http://rsb.info.nih.gov/ij/plugins/fft-filter.html
but I am not completely sure yet.

I think a low-pass filter can be achieved in the following way:
Let's say the image is 800x800 and only small objects with a size of a
few pixels, e.g. 3 pixels, are contained.
For a low-pass filter set the filter for large structures to 800 so
that low frequency signals pass and the filter for small structures to
3 in order to filter out high frequency signals.
Is this correct?

Would a high-pass filter then be achieved in the following way?
Set the filter for large structures to e.g. 3 and the filter for small
structures to 800.

Cheers,
Vincent

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