Photo editing without resolution loss

[kristaki]

So, I haven't quite found anything yet that edits photos and DOESN'T reduce the resolution by half or more. Lightbox has wonderful filters that make changing stuff easy and quick, but reduces the original resolution by at least half. Same with Vignette, and even Photoshop says it will have a max size of 1600x1600. I want to be able to do my editing on the go so that I can print large sizes without crappy results. Any ideas or anything coming down the pipeline that would suit those needs?