I've searched around, there's a few topics like this (including one i made myself a while back regarding lettering) but nothing that helps me with this specific problem, so i hope it's ok to post this - it's driving me crazy.
1) I did a drawing. Here's a piece of it so you know what kind of thing we're talking about here (just a black and white pen drawing):
2) I scanned it in.
3) Now, what i want to do is change the black line colour, lets say to bright green. I've found a couple of ways to do this, the easiest seems to be using the 'screen option'. (Layer of green over the top, screen option, merge the layers - voila a green line drawing on a white background.)
4) Now here's the problem. I want to drop my new bright green line drawing over a navy blue background.
I can't find a single way of doing this. Because it's hand drawn and not some vector image, there seems to be no way at all to remove the white without pixellation around the edges. Magic wand won't work, knocking it out won't work. I don't know how to turn it into a vector, and i wouldn't want to anyway as that would make it all crisp and shiny, which is not what i'm going for at all.
If i wanted a white background, no problem. Like i said, i could change the layer to 'multiply', and bam, green on white. I need something like this, that will allow me to drop bright colours over dark colours, whilst excluding the white.
If anyone could help me, i would be in your debt, i've been struggling with this for months, and i'm beginning to think it simply isn't possible