Posted by
Michael Schmid on
Oct 15, 2010; 8:01am
URL: http://imagej.273.s1.nabble.com/FFT-Bandpass-Filter-How-to-exclude-particles-or-other-foreground-objects-tp3686219p3686220.html
Hi Ovrec,
a Fourier transform always uses the full image, you can't exclude
areas from it. This also applies to filters in the Fourier domain.
If your objects are small enough, a simple approach would be the
'Fast Filters' with filter type 'Background from minima' and a radius
that is larger than that of all objects. The Fast Filters plugin can
also subtract the background from your image without an additional step.
What you could also do - this is more like your original idea:
- duplicate the image
- threshold the objects
- Create Selection from the threshold
- remove the objects useing several iterations of 'Fast Filters',
blur ('Border-limited mean') in x direction only (y Radius = 0)
- Use a Fourier filter (Custom Filter) that keeps the streaks instead
of removing them, i.e. a filter function with a vertical bar in the
center having a value of 255 (use Gaussian blur to avoid sharp edges)
- Subtract the result from the original.
(Instead of the Custom Fourier filter, you could also try the Fast
Filters, blur the full image in x direction to create the background.)
If it did not come with your distribution of ImageJ, the Fast Filters
plugin is available at
http://imagejdocu.tudor.lu/doku.php?
id=plugin:filter:fast_filters:start
Michael
________________________________________________________________
On 14 Oct 2010, at 15:03, Ovrec wrote:
> Hello everybody
> I'm using the FFT>Bandpass Filter to suppress horizontal stripes
> (streaks)
> in AFM images.
> Is there a way to exclude particles or other foreground objects
> from the
> fit? ...like selecting a threshold to include the background only
> and thus
> restricting the stripes suppression only to a selection (i.e., to the
> background).
>
> Thank you in advance
>
>
>
>
> -----
> Ovrec