The NN was explicitly trained for artifact-free PNG sources of anime fanart. Which it handles quite well according to my own testing[1]
Its benefits are questionable if used on anything else.
I've also tested it on anime screenshots and in that case it's it pretty much is en par there with NNEDI3 (which is computationally much cheaper) because real world encodes actually have compression artifacts and those get scaled too if you disable noise reduction or everything is smoothed out too much if you leave it on.
So if you want to use it on anything else you really do have to retrain the NN first, otherwise you get results you could also achieve by other means (e.g. warpsharp, NNEDI or Photoshop Topaz)
Also, waifu2x only scales luma. Its chroma handling is just regular upscaling (whatever imagemagick uses by default. I think), so even that part could be improved.
Its benefits are questionable if used on anything else.
I've also tested it on anime screenshots and in that case it's it pretty much is en par there with NNEDI3 (which is computationally much cheaper) because real world encodes actually have compression artifacts and those get scaled too if you disable noise reduction or everything is smoothed out too much if you leave it on.
So if you want to use it on anything else you really do have to retrain the NN first, otherwise you get results you could also achieve by other means (e.g. warpsharp, NNEDI or Photoshop Topaz)
Also, waifu2x only scales luma. Its chroma handling is just regular upscaling (whatever imagemagick uses by default. I think), so even that part could be improved.
[1] http://forum.doom9.org/showpost.php?p=1722990&postcount=3