For the contours you can see them applied on top of a normal volume rendering. I also made a mode where you only see the contours, and everything else is white. The contours use curvature estimation to create uniform thickness. They are also depth varying , so that lines further from the camera are a bit thinner.
The toon shading uses the colors from the transfer function, but divides the intensities into smaller sets of discrete colors. This makes the images look more cartoonish.
Here you can see a combination of the two techniques in one rendering.
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Morten Bendiksen : morten.bendiksen<at>gmail<dot>com