3 ms·

GIMP has a wavelet deconstruction option/plugin which breaks frequency bands into separate layers (like a stereo's multiband equilizer). You simply delete the l

by kortex 5y ago

GIMP has a wavelet deconstruction option/plugin which breaks frequency bands into separate layers (like a stereo's multiband equilizer). You simply delete the layer corresponding to the frequency component and bam, visual features at that scale vanish, preserving structure at all other scales. There's even more sophisticated wavelet denoisers out there that effectively do the black circle over peaks trick, but automatically and more precisely.

woliveirajr 5y ago
I used this to remove/reduce scars from some portraits. Many layers and then edit the desired spot (without removing the layers). Works like charm.
- capitainenemo 5y ago
  https://pixls.us/articles/skin-retouching-with-wavelet-decompose/ https://pixls.us/articles/skin-retouching-with-wavelet-decom... covered nicely here.
colanderman 5y ago
I did look at this. It seems pretty coarse though -- wavelets generally divide the spectrum into power-of-two frequency bands, and the Gimp is no exception it seems. Also of course you have to remove all higher-frequency bands as well, since the halftone dots have high frequency content at the edges of the dots. Trying it out now, I'm able to get a good result (to my eye) by deleting the top two bands, but it looks nearly identical to the article's blurring example. Upscaling the image first by 141% and deleting the same two bands, the dots start peeking through, but the result looks closer to the article's inverse FFT result -- minus the artificial edge contrast enhancement that came from the author's use of black (rather than grey) circles.
- capitainenemo 5y ago
  G'MIC (which is available as a gimp plugin) has the exact same reversible fourier transform as a layer in it as the Fiji software he referenced. You can do the exact same operations from the article (or any other edits/blurs/selections to the peaks). It's a bit cumbersome since you can't preview what you're doing, but quite workable. Was trying it out on his reference image this evening and got (IMO nicer) results fiddling with magic wand/fuzzy select/grow/shrink and various fills.
- kortex 5y ago
  Huh, interesting, thanks for trying that out! Yeah I forgot about the overtone frequencies of the halftone dots. Yeah I supposed you'd need a tool with a continuous wavelet transform and potentially a 2D one at that.

by kortex 5y ago

woliveirajr 5y ago

I used this to remove/reduce scars from some portraits. Many layers and then edit the desired spot (without removing the layers). Works like charm.

capitainenemo 5y ago
https://pixls.us/articles/skin-retouching-with-wavelet-decompose/ https://pixls.us/articles/skin-retouching-with-wavelet-decom... covered nicely here.

colanderman 5y ago

I did look at this. It seems pretty coarse though -- wavelets generally divide the spectrum into power-of-two frequency bands, and the Gimp is no exception it seems. Also of course you have to remove all higher-frequency bands as well, since the halftone dots have high frequency content at the edges of the dots. Trying it out now, I'm able to get a good result (to my eye) by deleting the top two bands, but it looks nearly identical to the article's blurring example. Upscaling the image first by 141% and deleting the same two bands, the dots start peeking through, but the result looks closer to the article's inverse FFT result -- minus the artificial edge contrast enhancement that came from the author's use of black (rather than grey) circles.

capitainenemo 5y ago
G'MIC (which is available as a gimp plugin) has the exact same reversible fourier transform as a layer in it as the Fiji software he referenced. You can do the exact same operations from the article (or any other edits/blurs/selections to the peaks). It's a bit cumbersome since you can't preview what you're doing, but quite workable. Was trying it out on his reference image this evening and got (IMO nicer) results fiddling with magic wand/fuzzy select/grow/shrink and various fills.
kortex 5y ago
Huh, interesting, thanks for trying that out! Yeah I forgot about the overtone frequencies of the halftone dots. Yeah I supposed you'd need a tool with a continuous wavelet transform and potentially a 2D one at that.