5 ms·

Frequency Domain Image Compression and Filtering

62 points by vonadz 6y ago

andreareina 6y ago
There was an article that demonstrated scratch removal by zeroing out (or was it blurring?) the its dual in the DCT domain. Unfortunately I can't dig it up.
- johndough 6y ago
  Here are a few resources for periodic pattern removal (e.g. in halftone print images) by zeroing out parts of the image in the Fourier domain. Maybe that was what you had in mind? http://matzjb.se/2015/08/08/smoothing-a-halftone-photo-using-fft/ http://matzjb.se/2015/08/08/smoothing-a-halftone-photo-using... http://scipy-lectures.org/intro/scipy/auto_examples/solutions/plot_fft_image_denoise.html http://scipy-lectures.org/intro/scipy/auto_examples/solution... https://developer.apple.com/documentation/accelerate/halftone_descreening_with_2d_fast_fourier_transform https://developer.apple.com/documentation/accelerate/halfton... https://stackoverflow.com/questions/29235421/find-proper-notch-filter-to-remove-pattern-from-image https://stackoverflow.com/questions/29235421/find-proper-not... https://stackoverflow.com/questions/34027840/removing-periodic-noise-from-an-image-using-the-fourier-transform https://stackoverflow.com/questions/34027840/removing-period... https://www.youtube.com/watch?v=yyox358zIRw https://www.youtube.com/watch?v=yyox358zIRw
  - willis936 6y ago
    I did exactly that in a grad level image processing take home final and got a 70. There were other corruptions in the image. The professor never taught anything about image correction or evaluating error, he wanted to see what I came up with. I still don’t understand that grade.
  - andreareina 6y ago
    Found it[1]. I misremembered a bit, they demonstrated how to remove periodic noise, then left "remove the string" as an exercise for the reader (bottom of the page). [1] https://legacy.imagemagick.org/Usage/fourier/ https://legacy.imagemagick.org/Usage/fourier/
ctchocula 6y ago
I enjoy reading this author's articles such as the one explaining auto-differentiation [1]. Before that, I tried to understand this survey on auto-differentiation [2], and it just didn't click for me. The analogy to imaginary numbers was perfect. [1] https://blog.demofox.org/2014/12/30/dual-numbers-automatic-differentiation/ https://blog.demofox.org/2014/12/30/dual-numbers-automatic-d... [2] https://arxiv.org/abs/1502.05767v4 https://arxiv.org/abs/1502.05767v4
djmips 6y ago
Great article. The author also links to Steve Brunton's video on A Compressed Overview of Sparsity. I found Mr. Brunton's channel only recently myself and found it to be a treasure trove of information. Highly reccomended. https://www.youtube.com/watch?v=aHCyHbRIz44&feature=youtu.be https://www.youtube.com/watch?v=aHCyHbRIz44&feature=youtu.be

62 points by vonadz 6y ago

There was an article that demonstrated scratch removal by zeroing out (or was it blurring?) the its dual in the DCT domain. Unfortunately I can't dig it up.

johndough 6y ago
Here are a few resources for periodic pattern removal (e.g. in halftone print images) by zeroing out parts of the image in the Fourier domain. Maybe that was what you had in mind? http://matzjb.se/2015/08/08/smoothing-a-halftone-photo-using-fft/ http://matzjb.se/2015/08/08/smoothing-a-halftone-photo-using... http://scipy-lectures.org/intro/scipy/auto_examples/solutions/plot_fft_image_denoise.html http://scipy-lectures.org/intro/scipy/auto_examples/solution... https://developer.apple.com/documentation/accelerate/halftone_descreening_with_2d_fast_fourier_transform https://developer.apple.com/documentation/accelerate/halfton... https://stackoverflow.com/questions/29235421/find-proper-notch-filter-to-remove-pattern-from-image https://stackoverflow.com/questions/29235421/find-proper-not... https://stackoverflow.com/questions/34027840/removing-periodic-noise-from-an-image-using-the-fourier-transform https://stackoverflow.com/questions/34027840/removing-period... https://www.youtube.com/watch?v=yyox358zIRw https://www.youtube.com/watch?v=yyox358zIRw
- willis936 6y ago
  I did exactly that in a grad level image processing take home final and got a 70. There were other corruptions in the image. The professor never taught anything about image correction or evaluating error, he wanted to see what I came up with. I still don’t understand that grade.
- andreareina 6y ago
  Found it[1]. I misremembered a bit, they demonstrated how to remove periodic noise, then left "remove the string" as an exercise for the reader (bottom of the page). [1] https://legacy.imagemagick.org/Usage/fourier/ https://legacy.imagemagick.org/Usage/fourier/

ctchocula 6y ago

I enjoy reading this author's articles such as the one explaining auto-differentiation [1]. Before that, I tried to understand this survey on auto-differentiation [2], and it just didn't click for me. The analogy to imaginary numbers was perfect. [1] https://blog.demofox.org/2014/12/30/dual-numbers-automatic-differentiation/ https://blog.demofox.org/2014/12/30/dual-numbers-automatic-d... [2] https://arxiv.org/abs/1502.05767v4 https://arxiv.org/abs/1502.05767v4

djmips 6y ago

Great article. The author also links to Steve Brunton's video on A Compressed Overview of Sparsity. I found Mr. Brunton's channel only recently myself and found it to be a treasure trove of information. Highly reccomended. https://www.youtube.com/watch?v=aHCyHbRIz44&feature=youtu.be https://www.youtube.com/watch?v=aHCyHbRIz44&feature=youtu.be