In case anyone is wondering, Waifu2X is still king
Waifu2X used to be the only solution but it's just not very convenient to use so I actually moved over to Photoshop's then new upscale feature for a while, and then there was this Gigapixel thing by Topaz labs. So I wondered, how do these upscale solutions compare?

Well I tried and I think the answer is actually pretty definitive, Waifr2X with the right model basically is producing perfect results, it's as if someone manually re-drawn the same image in higher resolution.

https://ibb.co/gzpwqHd

Topaz Labs Gigapixel is clearly designed for photos and not illustration, it likes to add detail that shouldn't be there and sometimes it confuses JPEG artifacts as detail.

Photoshop's own solution is not bad but it's just not as good as Waifu2X. at least it runs super fast compared to the rest.

BTW I also compared Photoshop versus Gigapixel on real life photos, there's almost no difference between the two, Gigapixel is like Photoshop but with a sharpening filter, it's not worth the money.
I've heard good thing about Topaz but I guess one would have to test it on anime images
Based on your sample (and your sample only as I only have Waifu2x on my computer), I think Topez's is actually not bad.

I would prefer Topez's over waifu2x's "oily (overfiltered feeling)" result if not for the artifact introduced by JPEG - which Waifu2x definitely has a lead on removing them.

Yes, the Waifu2x one is more "clean" but also it also loses lots of details (see the texture on her shoulder etc.).

I wonder if the source file is png, it may have even clearly better results than Waifu2x.
fireattack said:
Based on your sample (and your sample only as I only have Waifu2x on my computer), I think Topez's is actually not bad.

I would prefer Topez's over waifu2x's "oily (overfiltered feeling)" result if not for the artifact introduced by JPEG - which Waifu2x definitely has a lead on removing them.

Yes, the Waifu2x one is more "clean" but also it also loses lots of details (see the texture on her shoulder etc.).

I wonder if the source file is png, it may have even clearly better results than Waifu2x.
I'm pretty sure those are not "details" on her shoulder, they're just noise/artifacts, but I will do another test with very clean images and pure upscaling.

Here's the result:
https://ibb.co/ZmVzgBk

Topaz Labs and Photoshop somehow re-introduces jpeg artifacts into the image where none existed....

I also just tested straight up photograph, and there really isn't much of a difference. Gigapixel looks sharper but if you just sharpen the other two they basically look identical.
https://ibb.co/kmkjP5b
I insist that Gigapixel is just a scam, like many of their other filters.
Would be easier to tell if you can provide the original image (I can't find it via reverse image search), but yeah if that's the case, then these "details" are no good.

The waifu2x one still lost substantial details though (for example, the end of her eyelash on the right eye that extended to orange hair is totally gone), but that's more about the denoise pre-processing. That's why I normally won't use its denoise filter (but it's kinda unavoidable in order to get acceptable result if the source is noisy, admittedly).

> somehow re-introduces jpeg artifacts into the image

More like some haloing-like artifact due to the upscaling process, kinda common in traditional algorithms.
fireattack said:
Would be easier to tell if you can provide the original image (I can't find it via reverse image search), but yeah if that's the case, then these "details" are no good.

The waifu2x one still lost substantial details though (for example, the end of her eyelash on the right eye that extended to orange hair is totally gone), but that's more about the denoise pre-processing. That's why I normally won't use its denoise filter (but it's kinda unavoidable in order to get acceptable result if the source is noisy, admittedly).

> somehow re-introduces jpeg artifacts into the image

More like some haloing-like artifact due to the upscaling process, kinda common in traditional algorithms.
https://yande.re/post/show/515674

I see the eyelash thing, seems pretty minor to me, I ran the same image with less denoise strength, which does keep the eyelash but also kept some of the noise. I picked this image in the first place because it is the kind that I most desperately need good upscaler for, fantastic art but low res and jpeg only.

BTW the other algorithms were ran at the highest denoise settings.