WYSIWYG NPR: Interactive Stylization for Stroke-Based Rendering of 3D Animation (Thesis)

Abstract:

Artists and illustrators have developed a large repertoire of techniques to
communicate information effectively using traditional media. Recent work in
computer graphics has begun to leverage these techniques in the form of
non-photorealistic rendering (NPR) algorithms for 3D, but, to date, little
research has addressed flexible, interactive tools to make such algorithms
accessible to content creators. In this dissertation we demonstrate the
importance of developing these tools for NPR. In particular, we show that
“hands-on” NPR systems can provide the designer with new levels of aesthetic
flexibility, and the means to achieve effects tedious or even impossible to
attain by traditional methods.

We approach this open problem for stroke-based NPR of animated 3D geometry.
Our system employs a tablet interface to provide the designer with an
interactive paradigm in which stroke effects are sketched directly into the
scene. The artist imparts his unique aesthetic by sketching strokes over the
utlines of objects, and drawing details and hatching effects onto their surfaces.

These tools raise new questions regarding how annotations drawn by the designer
in one view should appear when the scene is rendered from novel viewpoints. It is
unreasonable to expect the user to annotate geometry from all conceivable poses.
Rather, we develop rendering algorithms that can exhibit a range of behaviors
which the designer can tune to specific goals, either by adjusting parameters or
directly sketching the desired effects. But it is not sufficient for the
stylization rendered in each frame to maintain consistency only with the
designer’s annotations. To be suitable for animation, they must also exhibit
coherence between consecutive frames. We consider this for all effects in our
system, but this is particularly challenging for those stylizing view-dependent
silhouettes. For these, we develop a flexible and robust new framework that can
provide coherence tailored to a particular aesthetic. These tools make possible a
new class of effects that would be daunting to animate by hand.

This research shares applications with those of traditional hand-generated
techniques, including architectural and product design, technical and medical
illustration, storytelling (e.g. children’s books), games, fine arts,
and animation.