Need help with specific Graphic Setting for maximum image quality

[LunaMoo]

The in-game textures are always very low res in PSP games, in many other games it's even worse. It might appear sharp on PSP, but if you run PPSSPP at x1 window size it would too.

The only ways to improve it would be texture upscaling, but in automatic form it's pretty meh as it doesn't fit most of the artstyle, other way would be to replace textures with higher res ones, good results for that required manual work in the past, but nowadays you can use some AI upscaling which tend to look nice and there are many variants of upscaling algorithms to try, texture replacement might not be easy for all games through, because some PSP games worked in very unconventional ways. If all you care about are screenshots you might as well AI upscale the screenshots themselves.