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Real-Time Image-Space Outlining for Non-Photorealistic Rendering
Author(s): Jason L. Mitchell, Chris Brennan, Drew Card.
Proceedings: Siggraph 02,
2002.
[BibTeX] 
Abstract:
In Non-Photorealistic Rendering (NPR), outlines at object silhouettes, shadow edges and texture boundaries are important
visual cues which have previously been difficult to generate in real-time. We present an image-space technique which uses pixel
shading hardware to generate these three classes of outlines in real
time. In all three cases, we render alternate representations of the
desired scene into texture maps which are subsequently processed
by pixel shaders to find discontinuities corresponding to outlines in
the scene. The outlines are then composited with the shaded scene.