The problem with most smartphone image editors is that they are meant for quick edits to photos. Usually they are limited to cropping, adding filters and drawing. I’m looking for something a little more capable, something more akin to a traditional desktop editor like GIMP. Open source is a plus.
I don’t know about open source, but the only Android app that comes anywhere close to the functionality of GIMP/Krita/Photoshop is Infinite Painter, AFAIK.