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by jeresig 4043 days ago
Yeah - the background looking like crumpled-up wrapping paper is definitely not ideal. I suspect that it's having trouble with mostly-uniform areas of color that have slight variations. It appears to be extrapolating and creating these larger effects.
2 comments
userbinator 4043 days ago
mostly-uniform areas of color that have slight variations

That's precisely what it's attempting to smooth over - and it works well for anime images because in them, those variations would be considered noise.

Wondering if it would anime-ise it, I fed Waifu2x the standard Lenna image - twice - ended up with this:

http://i.imgur.com/iNWRjIS.png

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Malcx 4043 days ago
How did you achieve that? I've run it through several times and whatever settings I use, can't get anything close to yours?
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userbinator 4043 days ago
I took the original, scaled it down to 1/4, and then back up to original with Waifu2x at 2x scale, maximum noise reduction.
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zellyn 4043 days ago
That's fantastic!
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sthatipamala 4043 days ago
Have you tried running the original through a high pass filter (to get the textures) and applying it over the vectorized version? It might work for the background texture, though it would probably suck for the text.
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jacobolus 4043 days ago
It would preserve all the JPEG artifacts, which are the main reason the naively upscaled version looks so crappy in the first place.
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astrange 4043 days ago
There are well-known techniques to clean JPEG artifacts, but they need the tables from inside the JPEG to work best.

Since JPEG uses an 8x8 block transform, you can find artifacts by shifting the image a few pixels over and looking for how the transformed block changes, basically.

https://github.com/FFmpeg/FFmpeg/blob/master/libavfilter/vf_...

Also, using a better chroma upscale can help for small images. libjpeg just uses nearest-neighbor (no "real" resizing) and hardly anyone notices, but it helps with lines and edges.

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jeresig 4043 days ago
I have not - although that's an interesting idea, thank you! Relative to my other projects this is a very low-priority exploration. I was very interested to see if there could be a "cheap win" for this particular sub-problem that I will be dealing with, should I get around to digitizing these books.
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