Re: Fourier filters
Posted by
Gluender on
Apr 19, 2007; 11:49am
URL: http://imagej.273.s1.nabble.com/Fourier-filters-tp3699723p3699726.html
Dear Sandro de Luelmo,
image filtering in ImageJ is possible in various ways.
The quickest but perhaps not the most educative way is to use the
"FFT > CutsomFilter..."-approach.
Open the filter function, make the image to be filtered the foremost
window and select the above menu. In the appearing dialog select the
filter function and there it is -- the filtered image!
Caution! The original image is overwritten by the result, so you
should use a copy of the image.
Make sure that image and filter functions are ( 2^n x 2^n )-sized!
>Hi my name is Sandro de Luelmo and Im working as a teacher and we
>are trying to use ImageJ as a pedagogical tool for our students.
>Its a course in image processing and we want them to understand the
>Fourier transform and how filtering in the frequency domain working
>in detail.
>
> An exercise that I would like to include could be as follows:
> The student should perform a FFT on a image. Save that FFT-image
>in there portfolio for later presentation. Open a high-pass filter
>and save the image of the filter for later presentation. Multiply
>the FFT-image with the high-pass filter and save the result-image
>for later presentation. Perform a INVFFT on the result-image and
>thereby obtain a edge enhanced image compared to the original image.
>
> Ive tried everything in ImagJ but it is for example impossible to
>multiply a FFT-image with a FFT-filter and then inversing it! Is
>there anyone that knows if it is possible to achieve the goals I
>have for this course? Maybe I could use some plugins or macros for
>this task??
>
> Best regards
> Sandro de Luelmo
There are other methods, especially the use of the plugin FFTJ, but
they require more preparatory work and especially a good
understanding of the essential differences between the FT and the
discrete FT or the FFT.
HTH
Best
--
Herbie
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