Posted by
Vincent Wolowski on
Dec 01, 2013; 5:54pm
URL: http://imagej.273.s1.nabble.com/Low-and-high-pass-filter-tp5005690p5005750.html
Hi Michael,
thanks a lot for your feedback!
As far as I can see the functionality of Process>Filters>Gaussian Blur
is based on the class ij.plugin.filter.GaussianBlur.
I have tested programmatically the filtering provided by the class
GaussianBlur with various different values for radius and accuracy
always set to 0.01,
and compared the results to the FFT filter of Joachim Walter provided
here:
http://rsb.info.nih.gov/ij/plugins/fft-filter.html in an
automatic fashion to find the best parameters.
I have read that applying the Fourier transformation and filtering in
the frequency domain is like a Gaussian smoothing in the spatial
domain.
However, in all the measures I used for comparison the above FFT
filter performed much better.
Have you experienced any differences when applying FFT filtering
compared to Gaussian blurring?
Might there be some implementation details that are different and that
could cause the different outcome?
Best regards,
Vincent
On Thu, Nov 28, 2013 at 9:57 AM, Michael Schmid <
[hidden email]> wrote:
> Hi Vincent,
>
> your question is not very clear...
> Anyhow, for more details on the Fourier-domain filter, see this recent post (beware of a possible line break introduced by the mailer in the link):
>
>
https://list.nih.gov/cgi-bin/wa.exe?A2=ind1311&L=IMAGEJ&D=0&1=IMAGEJ&9=A&P=187719>
> Essentially, you can do the same type of filtering with Process>Filters>Gaussian Blur (low pass) or subtracting the Gaussian blurred image (highpass). A high pass filter working like this is also available as a filter with preview:
>
http://imagejdocu.tudor.lu/doku.php?id=plugin:filter:highpass_filter:start>
> Michael
> ________________________________________________________________
>
>
> On Nov 25, 2013, at 14:02, Vincent Wolowski wrote:
>
>> Dear all,
>>
>> I am trying to understand how to use the Process/FFT/Bandpass Filter
>> for low- and high-pass filter on 16-bit images. I have read the
>> documentation here:
http://rsb.info.nih.gov/ij/plugins/fft-filter.html>> but I am not completely sure yet.
>>
>> I think a low-pass filter can be achieved in the following way:
>> Let's say the image is 800x800 and only small objects with a size of a
>> few pixels, e.g. 3 pixels, are contained.
>> For a low-pass filter set the filter for large structures to 800 so
>> that low frequency signals pass and the filter for small structures to
>> 3 in order to filter out high frequency signals.
>> Is this correct?
>>
>> Would a high-pass filter then be achieved in the following way?
>> Set the filter for large structures to e.g. 3 and the filter for small
>> structures to 800.
>>
>> Cheers,
>> Vincent
>
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