Rendered Cartoon Illustration Technique Part 1
So here we go. I do hope someone finds this useful. All I ask is that you please don’t copy this tutorial verbatim and reproduce it elsewhere. I’m happy to share for free, but I wish to keep my copyright. I’ve also published a similar tutorial of a simpler image in Corel Painter Magazine, issue 8, called “An Introduction to Airbrushing” for those who might be interested.
I start by taking my scanned line drawing and copying it to its own new layer, which I make a GEL composite method layer. 
This makes it transparent, and I can turn it on and off as a guide as my image develops. I also leave the original red scan as the Canvas layer.
I do a lot of work in this style using the Pen Tool. 
Drawing vector-based shapes takes practice, but there’s no better way to digitally create precise paths than this. Painter’s Pen Tool works pretty much the same way Illustrator’s and Photoshop’s does, placing straight-line points and allowing you to pull “handles” that control the curves.
What I’m really doing is the equivalent of “frisket” cutting for traditional airbrushing. I design these illustrations to be broken into a series of major shapes that will each be on its own layer.
Here you see the completed “Shape” path (look carefully - you can give these strokes and fills, but mine is just a path indicated in light blue with red points drawn to define the edges of the back-most flame shape). You can of course re-arrange layers easily, but I try to work logically “back-to-front” as I go.
Here I’ve converted the shape path to a selection. You can do this with a button on the Property Bar while the Pen Tool is selected , or from the Shapes Menu anytime the shape is selected. Selections are masks that control where digital “paint” or effects can go. The active selection is a moving dashed line sometimes called “marching ants”.
Now I fill the active selection with a flat color. You can use the Paint Bucket tool or go to Effects>Fill on the menu bar. At this point you can save the selection to the Channels palette, which I sometimes do, but often I don’t bother if the selection is ultimately going to be it’s own layer. This is because you can control where pixels go on a layer by using Preserve Transparency on the Layers Palette.
Here you see the filled shape layer and the Gel layer with the line drawing turned on. As I cover the Canvas layer, I can still see where I am by turning this on anytime I want. This will not be a part of the finished image.
Here I repeat the process for the next major area of flames. I don’t worry about the edges in common with the first shape, because I can load the selection to intersect with the transparency from the first shape’s layer. This gives a perfectly aligned edge when I fill it (as the second shot shows). I also don’t worry about edges that I know will be covered up by succeeding layers.
Here I’ve added a third shape layer over the last two.
I continue along using this method to establish the major elements of the illustration on layers. This is also a good way to begin creating your color scheme. Here is the progress with and without the Gel layer on. At this stage I already have 8 or 9 layers. Once I have this basic image, I’ll begin to add the details. We’ll talk about this in the next installment.