What free software do you prefer for image upscaling?

Question

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 · Accepted Answer

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.

rahimnathwani · Answer

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

crazypython · Answer

Imagemagick