Re: median filter that preserves peaks

Posted by John Dunsmuir on Sep 09, 2013; 3:02pm
URL: http://imagej.273.s1.nabble.com/median-filter-that-preserves-peaks-tp5004693p5004728.html

Neil,
       There have been a lot of good suggestions in this thread but it seems from your post that you are not quite where you want to be. So here is one more idea to try.  Perhaps a CFAR (constant false alarm ratio) filter might help pick the real target peaks that need to be preserved out of the noise. 2D CFAR is relatively easy to code and may be worth a try by itself or in combination with other techniques.

Regards,
John D.

Neil Fazel wrote

Thanks for the responses.

It seems to me that a generalized spatial filter (e.g. the "XXXFilter" suggested by Kenneth) might be the way to go.

I did give FFT a try and, after tweaking the parameters, got results matching what the median filter produced. However, it seems to me that one needs to be careful with FFT filtering. Sometimes high frequency components of the signal are noise and need to be removed. Sometimes they are actual signal and removing them biases the data. In such cases, a spatial filter such as mean or median may be appropriate. For example, in my case, I have x-ray which is filtered by Cu or Al and recorded on an imaging plate. What looks like noise could in fact be from sideways scattering of x-rays inside the filter pack. One needs to determine whether such signal should be removed (via FFT filter) or merely smoothed (via mean or median filter) to make analysis easier.

Regards,
Neil

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