In this example, I've used a picture drawn in
Adobe Illustrator. Whilst it is entirely possible to both
draw and colour your artwork in this package, the technique
being demonstrated here requires the use of Photoshop or an
equivalent. If you would like to experiment with this file,
the .ai version is available as a download at the bottom of
the page.
First of all, select
your entire line drawing, making sure that there are no
fills, just the lines, and copy it. Take it into Photoshop,
and open a new document in RGB mode with a white background.
I always add 20 pixels or so to the height and width
generated by the computer so the image isn't pushed right
against the edges. Place the image in the centre of the new
document and OK it. The line art should now be on one layer,
whilst the white background is on another.
[
you'll be making something similar to what is
shown above ]
Create a new
layer in between these to - this is what we're
going to colour on. There are basically two
methods of doing this. For the larger areas, use
the Magic Wand tool to select a section inside the
lines layer.

[ select an area with the
Magic Wand ]
Without losing the
selection, move down to the new empty layer. Use the colour
picker to choose the shade you want, the Fill. Notice that
because the lines layer is on top, you don't have to worry
about going over the edge slightly. If the Wand has missed
an area, then use the Brush tool to tidy it up, on around a
1 - 3 pixel setting.

[ use the Fill tool to colour
]
At this stage, don't
worry about shading your picture, just concentrate on
building up the basic blocks of colour.
For smaller, more
detailed sections, it's easier to use the Brush tool from
the outset. Just make sure you colour in between the lines,
using the top most layer as your guide. Once finished, you
should have something looking like the image below.

[ image with base colours
filled ]
Now make a fourth
layer, on top of the colours, but beneath the lines. This is
where you will add the shading. To do this, use the
Eyedropper tool to pick up the base colour of an area, then
open the colour mixer. Select a tone that's darker than the
original, then go back to your image. Use the Brush (on
around 3 pixels) to gently add shadow. Use the lines as a
guide - if you have drawn a fold in some clothing for
example, then you will need to add shadow to this area. Pick
a direction for a light source before you start shading, as
this will help you work out where the shadows will be
falling. If you included shadows on the original sketch, now
would be a good time to refer back to it.
The hair is often a
tricky area, because of the highlights, however there is a
simple method for getting a good result. Add the shadows as
normal, then make another layer on top (in case it doesn't
work out right the first time). Pick up the base colour
again, only this time choose a much lighter shade. Again
with a small brush, carefully draw some areas of highlight.
This usually follows a circular path round the head,
although may vary depending on your drawing. Once in place,
use the Smudge tool to smear the edges, blending it in with
the base a little more.

[ adding a highlight to the
hair ]
Choose an even lighter
colour, then add a very thin line with the Brush to the
middle of the highlight. This should give the overall effect
of light falling onto the hair. Merge this layer with the
shadows layer when you are satisfied.

[ the finished image ]
That's pretty much all
there is to it. Make sure that all the layers are visible
and Save For Web. Keep a copy of the .psd file too, in case
you wish to come back to it later.
A nice effect can be
achieved by linking the two coloured layers and shifting
them off by a couple of pixels. This slightly mis-aligns the
fills, creating a more cartoon-ish look and feel.

[ image with fills out of
alignment ]