Fourier Transform tutorials

[Leader344]

Hi. I am a novice GIMP user. I have 2.10.8 and G'MIC. Retired, I look at GIMP as a way to stay "mentally challenged". One thing I like to work on are old family pictures, with some having the coherent noise patterns that I thought Fourier Transform could improve. I have watched youtube videos on G'MIC Fourier Transform, but the tutorial directions I've found don't align with what I see in G'MIC - Frequencies - Fourier Transform. Could someone direct me to tutorials or instructions that align with the Fourier Transform I see in 2.10.8?  THANKS for any information or suggestions!!!

[rich2005]

I can do a quick demo of the G'mic version.





duration 2 and a half minutes.

If you give details of OS I might be able to suggest a different version.

[Leader344]

(11-11-2019, 09:29 PM)rich2005 Wrote: I can do a quick demo of the G'mic version.





duration 2 and a half minutes.

If you give details of OS I might be able to suggest a different version.

Rich. Thanks for the quick response. After viewing, this is a great FFT start for me. My OS is Windows 10 - 64 bit. My GIMP is 2.10.8. If you have other versions to suggest, I will definitely give them a try. Thanks again!

[rich2005]

You can try the more usual FFT plugin. This one 64 bit for Windows.

Unzip the attached file and put the whole folder fourier (which contains two files,  fourier.exe & libfftw3-3.dll ) in your Gimp profile C:\Users\"yourname"\AppData\Roaming\GIMP\2.10\plug-ins .

The plugin shows in Filters -> Generic -> FFT Forward (and FFT Reverse) 

Apply FFT Forward to your image. The FG color is automatically changed to the correct grey. There is no selection to worry about, you can apply a Transparent-to-Grey gradient same as with the gmic filter. When finished apply FFT Reverse to get back to your image.

Some  images have noticeable defects in the FFT image. You can paint these out instead of applying a gradient. Sometimes gives better results.

Example: some screenshots
https://i.imgur.com/U1EAfAn.jpg
(1) This has a regular pattern - from a scanned magazine image.
(2) Applied FFT Forward and painted out some of the defects (red X ) still have magenta to paint out. Keep away from the center or you will totally blur Otherwise you do not have to be very accurate.

https://i.imgur.com/YR15Ul7.jpg
(3) Completed painting out the defects - dotted round so you can see them
(4) Applied FFT Reverse

[Leader344]

Rich. Thanks for your support! With your help, I now have the FFT, Resynthesizer, and Heal Selection plugins in Gimp.

[Ofnuts]

(11-19-2019, 08:50 PM)Leader344 Wrote: Rich. Thanks for your support! With your help, I now have the FFT, Resynthesizer, and Heal Selection plugins in Gimp.

For your intellectual challenges, a fascinating video on the Fourier Transform: