Dahaka

First, before I ask anything, I have to say that I love paint.net. It's better than the Gimp in my opinion, by far! I've been trying to complete many signatures latley, but I've come across a problem. When I get my render, it usually comes with a black background, and I really want to be able to get rid of that back blackground so that the render itself is on a BLANK background. I feel like a total noob for posting this but I can't seem to solve it!