I finally packed my image filtering library into a Paint.NET Plugin which can be downloaded here : 2dImageFilter.
This library contains all of the standard algorithms used in various emulators (like VirtualGB, Mame, DOSBox, SNES9x, ZSNES to name some of them).
I adapted them to be used not only on pixel graphics by giving them the ability to identify pixels that are alike and not exactly the same color. They will interpolate on matches to give slightly better results than their original. Even