frequency spectrum

classic Classic list List threaded Threaded
2 messages Options
Reply | Threaded
Open this post in threaded view
|

frequency spectrum

julio buonfigli
Hello everyone, I am looking for a function like a FFT (forward fourier transform) but not exatly. I need a frequency spectrum like the one I would get from a sound signal, namely, the intensity of every frequency but no information about the phase. I want to compare two images, for example two cells, to know if both cells have the same features relative to the size of vesicles (I expect this would be a specific frequency) and general organization (other frequencies). With FFT I can not compare because on the transformed image the frequency peaks appear on different sites according the spatial distribution of the spatial domain image. Any tip?      

--
ImageJ mailing list: http://imagej.nih.gov/ij/list.html
Reply | Threaded
Open this post in threaded view
|

Re: frequency spectrum

Michael Schmid-3
Hi Julio,

seems you need the power spectrum, and then a radial plot.

(i) Select the Power spectrum in Process>FFT>FFT Options
   The "normal" FFT display has logarithmic scaling of the pixel value
(with autoscaling, so one can't determine what pixel range corresponds
to e.g. one decade of power spectrum values)

(ii) Radial profile plugin, e.g. this one:
      https://imagej.nih.gov/ij/plugins/radial-profile.html
    Select the whole PS image.
You will probably have to adjust the y range of the plot; logarithmic y
axis may help (More>>Set Range)


Michael
________________________________________________________________
On 04.12.18 15:09, julio buonfigli wrote:
> Hello everyone, I am looking for a function like a FFT (forward fourier transform) but not exatly. I need a frequency spectrum like the one I would get from a sound signal, namely, the intensity of every frequency but no information about the phase. I want to compare two images, for example two cells, to know if both cells have the same features relative to the size of vesicles (I expect this would be a specific frequency) and general organization (other frequencies). With FFT I can not compare because on the transformed image the frequency peaks appear on different sites according the spatial distribution of the spatial domain image. Any tip?
>
> --
> ImageJ mailing list: http://imagej.nih.gov/ij/list.html
>

--
ImageJ mailing list: http://imagej.nih.gov/ij/list.html