[FRIAM] Fourier image space, duality, filtering and compression

[Stephen Guerin]

Jon, Mike and I were talking about fourier transforms on images, JPEG
compression and filtering at this morning's FRIAM.

Here's a nice site that lets you load an image, and its fourier transform
(amplitude spectrum) in cartesian or log-polar.
     https://www.djmannion.net/img_freq_web/

 A menu allows you to pull up sample images, simple sine waves in various
frequencies and orientation and a live webcam image to see their point
dualities in fourier space.

The lower panel lets you filter high and low cutoffs (much like jpeg
compression) to see the impact on the image.

links related to compression:

https://blog.demofox.org/2020/11/04/frequency-domain-image-compression-and-filtering/

https://micro.magnet.fsu.edu/primer/java/digitalimaging/processing/fouriertransform/

different but related use of fourier transform for finding epicycles in a
drawing:

   - https://www.jezzamon.com/fourier/
   - https://www.myfourierepicycles.com/


-S


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