Because I have been asked for another photoshop tutorial, and because I have some free time to kill, I've decided to update my previous one, which was pretty confusing and round-about. This one will tell a much simpler way for preserving lineart, as well as some other tricks I've picked up recently. I only spent about 15 minutes drawing this, so I'm sorry that it's all in pencil not really clean looking. FYI, I use Photoshop 6, if you use 5 or lower, some of these things might now be exactly the same.
Step one: Making a lineart layer. Making sure your lineart is preserved is essential to coloring and scanned image, first scan the image. I ususally do 300-400 dpi grayscale. Your image should look something like this. A bit smudgey right?
Therefore we adust the levels by pressing ctl+L (apple+L for you mac users). This should bring up the following window.
Click on the white eyedropper (circled in red) and using the eyedropper tool, click on the darkest gray you want to erase from your drawing. If you click on a pure white pixel, this does nothing, and if you click on pure black, it erases everything, This is useful for getting rid of unwanted smudges or stray pencil lines that are lighter than the lineart. Next, click on the black dropper (circled in blue) and click on the lightest gray you want darkened, this will make your lineart stand out more. You can also manipulate the levels with the three triangles along the bottom of the graph, but using the eyedropper is quicker and more efficient. Here is a progression of using the white dropper and then the black dropper.
Ok, now you have some nice cleaned up lineart. You want to preserve that lineart so you can color beneath it. first right click on the text of the background layer (boxed in red, and select "duplicate layer" this will make an exact copy of your background layer. Select Layer<Layer Properties... and rename the layer as "lineart"
Next, double click on the lineart layer to get the Layer Style, go to the blende mode option and select "multiply". (red box) This makes all the white in your lineart layer transparent. Try to think of it as a transparency sheet placed on top of the background layer with the lineart drawn in black on it. create a new layer underneath the lineart layer and name it color, or whatever you want to. This is where you'll be adding the color. You might notice that your drawing's outline seems darker. Don't worry. If you clear out your background layer it will look like it did before. You don't need it anymore anyway.
See that wasn't too hard. And much easier than that Channel crap I had in my last tutorial. You'll find this much easier to deal with.