Coloring a cartoon in Photoshop
First, I sketch out the drawing normally with a Sharpie pen and scan it in. Use Photoshop tools to keep the contrast very sharp and to eliminate any smudges, scan edges, etc.
Create a new layer. I created new layers for each new color, which is what I recommend, but you don't absolutely have to do that. The most important thing is to choose "Multiply" in the Layers panel. This allows the black lines of the layer below to show through, that is, the color doesn't completely cover it up. Select a brush that is comfortable and start coloring. You can change the size of the brush to fit into small areas, but in a cartoon you want it to be kind of loose or it will look stuffy. Use the eraser tool if you make a mistake or just to clean up a bit if you go over the lines.
If you use separate layers for each color, which I did, you can go back and refine more easily. In fact, it's tempting to go on refining and refining until you have ruined it. I once had a painting teaching who recommended that you know when to stop. If you are trying to finish your painting, he said, you might "finish it" - kill it.
Save it as psd file so you can go back and make changes if you need to and save for web as a jpeg to optimize for the web.
Posted by Brad Hall