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Comment by cat9 | Hacker News Reader

Maybe? I'm definitely biased in that I have substantial computer vision & image processing experience, but the output looks riddled with obvious filter and vectorization artifacts to me.

Re: Image 2, http://i.imgur.com/541uG5t.png

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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.

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

How did you achieve that? I've run it through several times and whatever settings I use, can't get anything close to yours?

I took the original, scaled it down to 1/4, and then back up to original with Waifu2x at 2x scale, maximum noise reduction.

That's fantastic!

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.

It would preserve all the JPEG artifacts, which are the main reason the naively upscaled version looks so crappy in the first place.

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.

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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