actually I don't use anything on the computer. i just use paint to change file types. with this one I needed to darken the sketch so I tried this one time editing thing. the original sketches are much better I assure you, they're just too light for pd. *sigh* i kinda hate computer editing programs. the eat my art.
If you use something better than gimp, you can tinker with levels which darkens your black and greys seperatly. Also, if you have a good program, you can scan big, and shrink to a smooth look. You can't do that with paint cause paint doesn't do a gradual reduction. It's all on a 1 or the other basis. Look into Gimp. Seriously