Gradient Space Projection
These images are rendered using my global illumination renderer plug-in for 3D Studio Max R4
(native renderer of R4 did not have global illumination support).
It uses a special form of rasterization, Gradient Space Projection, instead of ray tracing.
In the left image, only a single light source is used (the lamp in the corner)
and almost all of the scene is illuminated by the reflected illumination from the ceiling.
The right image shows Gradient Space Projection used for gathering illumination from a photon map.
Abstract
Gradient Space Projection is a simple method for handling projections on the hemisphere. The proposed method defines a coordinate system on the hemisphere surface that effectively converts the hemisphere to an infinite plane tangent to the top of the hemisphere, which is called the gradient space. Using this coordinate system, projections onto the hemisphere are replaced by simple perspective projections onto the gradient space. This approach totally eliminates the non-linearities caused by the spherical surface and permits exact hemisphere projection computations using only a single projection operation.
Images
Here are two other scenes illuminated by a skylight
rendered using my old renderer plug-in for 3D Studio Max R4.
Videos
A simple animation showing the gradient space project in action. The motion is hand animated in 3ds Max R4 and rendered using my renderer plugin with global illumination support using gradient space projection in 2003.
Paper (Preprint)
BibTeX