Everyone has there own way of converting a sketch to a computer illustration. I'm not saying my way is the best but I have learned this technique by a combination of trial and error and reading similar tutorials by other artists, so I think it's time I contributed to the pool of knowledge.
Let's start with a pencil sketch:
Next I have roughly inked the lines- rough, because I will sort them out later. Then clean up the background a bit. I've done this by adding a mask to the layer and painting out the rubbish. This way I can just draw around the shape of my figure and 'fill' the space outside with the paintbucket tool.( You can also just use the eraser here if you prefer). Now go to Image/Adjustment/Levels and move the sliders about until you can't see the pencil lines.
So you have a clean black line that shows the figure. Now comes the really good bit:
Make sure your image is in RGB mode (Image/Mode/RGB color).
Open the Channels pallette and you should be able to see each of the three Red, Green and Blue channels. Hold down the 'control' button and click on the Blue channel. You now have marching ants selecting everything but the line of our drawing.
Go to the menu bar again and Select/Inverse selection. Now to save this selection because it can come in handy later, look at the bottom of the channels pallette and you should see some wee symbols. Click on the second one (a square with a circle cut out of it) and you have saved the selection as an alpha channel.
Now open the Layers pallette. Add a layer above the existing one.
Change the foreground colour to 15% Cyan.
Make sure your selection is still active, and that you are in the new layer, and while holding down the 'control' button press backspace to fill the selection with the Cyan.
Now delete the original image below and flatten the whole thing.
Get some decent quality illustration paper, I use Bristol Board, and print your line with your desktop inkjet.
Now you have a pale blue line on illustration board that you can ink to your hearts content.
Once you have it looking the way you want, scan it back into Photoshop.
Follow the steps above that we used to make the blue line, but this time create two layers above the background and instead of filling the top one with blue, use a black line.
Name that layer 'line drawing'. (It's a really good habit to develop because as the layers become more complicated you will be glad you know what's what.)
Name the middle one 'flat colour'
Delete the background.
So you have a lovely line drawing floating above the background with a clear layer inbetween.
Whip out your wand tool, make sure you are on the 'line drawing' layer and select the skin of the subject (or whatever you like but I'm starting with his face to illustrate the point). Now Select/Modify/Expand and click. In the pop-up box pick 2 pixels. (This puts your colour selection below the line drawing without any gaps)
Go over to the 'channels' and save this selection as an alpha channel, but also double click where it says 'alpha 1' and re-name it 'skin'. Go over the whole drawing doing the same thing so that each area where you will be adding colour has a corresponding alpha channel.
At this point I often visit the fantastic Adobe Labs 'Kuler' site. Here you can find the colour scheme you want to apply to your illustration and download it as a palette.
Ok, you have your alpha channels, and your line drawing is floating above your flat colour layer, so now go to that layer. This bit is now fast and simple, select each area by control clicking on the corresponding alpha channel and fill the shape with the colour you chose (again just hit backspace).
There you are- one beautifully coloured cartoon.
Now I usually start adding some tone.
Add a layer above the other three and name it shade.
Change the mode in the dropdown box to 'multiply'.
Select each area again with your alpha channels and drop in a slightly darker version of the tone already there. At this stage you can judge how dark you want this to be by changing the opacity slider of the layer.
Using the pen tool draw the shape you want to remove (or the shape you want to have as shadow and invert the selection later).
Once you have the shape, click the small dotted circle at the bottom of the 'paths' palette to convert to a selection and use it to delete the unwanted portion from your 'shade layer'.
You can also feather the selection before you delete if you want a softer edge to your shade.
To add light just repeat the above steps but instead of 'multiply' use 'screen' and pick a light shade.
For a finishing touch use a 'curves' adjustment layer to boost the contrast and intensify the colours.
And that's it. It might seem overly complicated but it does give you complete control over the process and allows you to get your artwork looking exactly the way you want.
I created a few simple shapes in Illustrator and imported them into the drawing - did a little dodge and burn and some adjustment layers to get the colour right and copied and warped a few of the pallettes and elements from the process above and this is the finished result.
I hope this is of some help and feel free to drop me a line and tell me what you think.
