Re: FFT-bandpass filter: exact meaning of low- and high-pass thresshold

Posted by H. Gluender on Sep 05, 2006; 3:16pm
URL: http://imagej.273.s1.nabble.com/FFT-bandpass-filter-exact-meaning-of-low-and-high-pass-thresshold-tp3701667p3701668.html

>Hello,
>I am just starting to use ImageJ for Image analysis and I am really
>impressed by the various functionalities.
>Particularily I want to convolute images with a defined convolution kernel.
>This is where I have my question:
>To my understanding a convolution with a gaussian kernel can be
>accomplished by the Process -> FFT -> Bandpass Filter menu.
>There you can input the thresholds for large and small structures to be
>filtered out.
>My question: What exactly do those number mean? Or more precisly the
>function effectivly performs a convolution of the image in real space with
>a gaussian kernel of a given size (well actually two kernels one for the
>large and one for the small structures).
>What is the relationship between the threshold you enter in the menu and
>the size of the gaussian kernel in real space.
>For example is it the FWHM (full width half max) or is it the standard
>deviation of a normalized gaussian distribution?
>
>Thanks in advance for any hints
>Jan-Peter

Did you look at

<http://rsb.info.nih.gov/ij/plugins/fft-filter.html>

as recommended in the ImageJ-manual?

Best
--


                   Herbie

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