Doctor's Theses (authored and supervised):
"Efficient Physically-based Shadow Algorithms";
Supervisor, Reviewer: L. Savioja, X. Decoret, M. Wimmer;
Helsinki University of Technology,
oral examination: 2006.
This research focuses on developing efficient algorithms for computing
shadows in computer-generated images. A distinctive feature of the shadow
algorithms presented in this thesis is that they produce correct, physicallybased
results, instead of giving approximations whose quality is often hard
to ensure or evaluate.
Light sources that are modeled as points without any spatial extent produce
hard shadows with sharp boundaries. Shadow mapping is a traditional
method for rendering such shadows. A shadow map is a depth buffer computed
from the scene, using a point light source as the viewpoint. The finite
resolution of the shadow map requires that its contents are resampled when
determining the shadows on visible surfaces. This causes various artifacts
such as incorrect self-shadowing and jagged shadow boundaries. A novel
method is presented that avoids the resampling step, and provides exact
shadows for every point visible in the image.
The shadow volume algorithm is another commonly used algorithm for
real-time rendering of hard shadows. This algorithm gives exact results and
does not suffer from any resampling problems, but it tends to consume a
lot of fillrate, which leads to performance problems. This thesis presents a
new technique for locally choosing between two previous shadow volume
algorithms with different performance characteristics. A simple criterion
for making the local choices is shown to yield better performance than using
either of the algorithms alone.
Light sources with nonzero spatial extent give rise to soft shadows with
smooth boundaries. A novel method is presented that transposes the classical
processing order for soft shadow computation in offline rendering.
Instead of casting shadow rays, the algorithm first conceptually collects every
ray that would need to be cast, and then processes the shadow-casting
primitives one by one, hierarchically finding the rays that are blocked.
Another new soft shadow algorithm takes a different point of view into
computing the shadows. Only the silhouettes of the shadow casters are used
for determining the shadows, and an unintrusive execution model makes
the algorithm practical for production use in offline rendering.
The proposed techniques accelerate the computing of physically-based
shadows in real-time and offline rendering. These improvements make it
possible to use correct, physically-based shadows in a broad range of scenes
that previous methods cannot handle efficiently enough.
Created from the Publication Database of the Vienna University of Technology.