Ask HN: What free software do you prefer for image upscaling?

[hnarn]

There are plenty of proprietary online resources for image upscaling, and they seem to do a decent job, especially for paintings or drawn content: examples include bigjpg.com, icons8.com etc.

I'm curious what these services are using as a back-end, are there any free alternatives that they might be using, or are most of them proprietary?

[brudgers]

I don't upscale images, but my first thought is ImageMagick. Googling "upscale imagemagick" seemed to indicate that it is suitable for the task.

More generally, upscaling is probably going to be >95% established algorithms with at best a small amount of perceptual heuristics to accommodate human vision. But I wouldn't expect perceptual heuristics to be common outside of tools like Photoshop because most of the time it won't matter and SEO is going to generate more revenue for a web service than quality.

I doubt there's much proprietary technology, it's understanding graphics sufficiently to make good judgements that's going to be rare.

[hnarn → brudgers]

I'm not exactly sure how these sites work, but they're clearly doing something different from "regular" upscaling like what happens when you just make a picture larger and blurrier, it looks like some kind of semi-vector type conversion before the resizing, but it's never described beyond the regular AI/ML buzzwords.

The reason I ask is because it could be really useful for stuff like wallpaper resizing where the only thing you really want is for the larger size to look decent, not necessarily be exactly like the original.

[brudgers → hnarn]

My google suggested unsharp masking was a useful transform.

[rahimnathwani]

https://github.com/nagadomi/waifu2x is good for line drawings

[crazypython]

Imagemagick

[hnarn → crazypython]

Could you briefly comment on how one would use imagemagick to do “smart” upscaling rather than the regular type that makes a larger and blurrier picture? Or is it smart by default?

I’ve barely used it so I’m not sure what to look for to figure this out on my own.

[tdeck → hnarn]

Here are some options from the IM docs:

https://legacy.imagemagick.org/Usage/resize/#adaptive-resize

Be sure to scroll down to liquid rescale also.