So I took a picture at a high ISO value in poor light conditions. I can't retake it, the grain effect is bad, I'm aware this will never be a good photo, but I still want to make the best out of it. So, photo-editing software and... then what?
What filters/tools/techniques to apply to maximally reduce the ISO noise and restore the image to maximum clarity?
GIMP preferred, though if you know good techniques that work with other open source software, please share too.