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PhD Thesis Computer-Generated Pen-and-Ink Illustration

Author(s): George Winkenbach.
PhD Thesis: University of Washington, 1996.
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Abstract:
This dissertation describes the principles of pen-and-ink illustration, and shows how a great number of them can be implemented as part of an automated rendering system. Illustration techniques in general, and pen-and-ink rendering in particular, offer great potential for creating effective images from CAD models. And with the computer’s ability to manipulate increasingly large models, communicating complex information in an effective and comprehensible manner is becoming an important problem. However, this potential remains relatively untapped in the field of computer graphics. After discussing principles of traditional pen-and-ink rendering, this dissertation shows how the traditional graphics pipeline must be modified to support pen-andink rendering. Then, it introduces the new concept of prioritized stroke textures. Prioritized stroke textures form the central mechanism by which strokes are generated so as to both convey a certain texture, such as “bricks”, and achieve a target tone simultaneously. Prioritized stroke textures also have the advantages of being resolution dependent; that is, they take into account both the resolution of the target device, and the size of the image when generating the strokes. A mathematical framework, and algorithms derived from it, for mapping stroke textures on parametric free-form surfaces are also introduced. Rendering strokes on parametric surfaces is not a simple problem, because the orientation of the strokes must indicate the shape of the surface, in addition to accurately reproducing tone and conveying texture. The solution proposed in this dissertation generalizes the concept of prioritized stroke textures and allows the use of traditional, image-based, texture mapping techniques. Thus, it extends considerably the range of effects that can be achieved with stroke textures. Finally, this dissertation describes two methods for building two-dimensional spacial subdivisions of the visible surfaces from the 3D geometry. These “planar maps” are needed during the rendering process for generating the outlines of the visible surfaces, while taking into account adjacency, tone, and texture information. The first method is relatively simple to implement, but is best adapted to polygonal models. The second method is more appropriate for models containing free-form surfaces.

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