Emulator

Could you post a screenshot?

Also, it would be very helpful if you could test this in 5.0, since it uses a different way of loading PNG files.

After some research I found out the issue I'm having started with the following change

• Use simplified libpng PNG reading API to avoid PNG reading bugs. (PR #7341 from AdmiralCurtiss)

It doesn't appear in build 5.0-8596 which was published before the change.

To clarify, I tested build 5.0-8596 and the issue was not present, no artifact.

My tests were done with PNG's from (the) GIMP's export function as well as Adobe Illustrator's, both produce a RGB image with 8-Bit alpha.

I tested Dolphin 5.0-8715 with your edited texture and there was no artifact. What's weird is that build 5.0-8596 and some earlier versions can load the original texture fine. To me it does still look like some useful code was lost in the simplification of PNG loading as even Adobe Illustrator created PNG files are "problematic" in this case.

The older versions appear the load the texture fine because their handling of transparency is nominally incorrect, which breaks other things. See issues like:

https://forums.dolphin-emu.org/Thread-hd-texture-problems
https://bugs.dolphin-emu.org/issues/11279
https://bugs.dolphin-emu.org/issues/11351

This 'color value of transparent pixels' is a thing that is somewhat specific to game development and can also happen in real games. Here's a good article about it: http://www.adriancourreges.com/blog/2017/05/09/beware-of-transparent-pixels/

A lot of programs fail to handle this sensibly by default because it's only ever apparent when you try to interpolate with the resulting image, which rarely happens outside of video games, and in practice you gain better image compression by discarding the color value of completely transparent stuff.

Very interesting read, it's a very specific problem I never heard about until now :)

Discarding color from alpha in Gimp's export function seems to do the trick too.