Fourier filters

[Sandro de Luelmo]

Hi my name is Sandro de Luelmo and I’m working as a teacher and we are trying to use ImageJ as a pedagogical tool for our students. It’s 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.
   
  I’ve 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

       
---------------------------------

Stava rätt! Stava lätt! Yahoo! Mails stavkontroll tar hand om tryckfelen och mycket mer! Få den på http://se.mail.yahoo.com

[Gluender]

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 I’m working as a teacher and we
>are trying to use ImageJ as a pedagogical tool for our students.
>It’s 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.
>  
>   I’ve 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

... [show rest of quote]

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

          ------------------------

          <http://www.gluender.de>

[Jan Eglinger-5]

Dear Sandro,

there is a nice Java applet demo of how FFT works at:

http://homepages.inf.ed.ac.uk/rbf/HIPR2/fftdemo.htm

Maybe it's useful for your course?
Best regards,
Jan

-------- Original Message  --------
From: Sandro de Luelmo <[hidden email]>
To: [hidden email]
Subject: Fourier filters
Date: 19.04.2007 11:27

> Hi my name is Sandro de Luelmo and I’m working as a teacher and we are trying to use ImageJ as a pedagogical tool for our students. It’s 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.
>    
>   I’ve 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
>
>        
> ---------------------------------
>
> Stava rätt! Stava lätt! Yahoo! Mails stavkontroll tar hand om tryckfelen och mycket mer! Få den på http://se.mail.yahoo.com

... [show rest of quote]

--
Jan Eglinger
PhD Student, Eckhard Lammert group
Max Planck Institute of Molecular Cell Biology and Genetics
Pfotenhauerstrasse 108
01307 Dresden
Germany

Tel:  [phone]
VoIP: [hidden email]

[Robert Dougherty]

Sandro,

How about this?

newImage("filter", "32-bit Black", 512, 512, 1);
run("Multiply...", "value=0.0000");
run("Add...", "value=1");
makeOval(178, 178, 154, 154);
run("Multiply...", "value=0.0000");
run("Select None");
run("Gaussian Blur...", "radius=20");
run("Bridge (174K)");
run("FFT Options...", "  complex do");
imageCalculator("Multiply create 32-bit stack", "Complex of
bridge.gif","filter");
//run("Image Calculator...", "image1=[Complex of bridge.gif]
operation=Multiply image2=filter create 32-bit stack");
run("Inverse FFT");

Bob

-----Original Message-----
From: ImageJ Interest Group [mailto:[hidden email]] On Behalf Of Sandro
de Luelmo
Sent: Thursday, April 19, 2007 2:27 AM
To: [hidden email]
Subject: Fourier filters

Hi my name is Sandro de Luelmo and I’m working as a teacher and we are
trying to use ImageJ as a pedagogical tool for our students. It’s 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.
   
  I’ve 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

       
---------------------------------

Stava rätt! Stava lätt! Yahoo! Mails stavkontroll tar hand om tryckfelen och
mycket mer! Få den på http://se.mail.yahoo.com