An improved illumination model for shaded display

@inproceedings{whitted1979improved,
  title={An improved illumination model for shaded display},
  author={Whitted, Turner},
  booktitle={Proceedings of the 6th annual conference on Computer graphics and interactive techniques},
  year={1979}
}

Original paper on ray tracing with global illumination.

Ray-Tree

extending from the viewer to the first surface encountered and from there to other surfaces and to the light sources.

Algorithm:

• create ray tree with hit informations for all pixels
• pass the whole tree to the shader
  • Shader traverses the tree to deterimine final color

Consideration of all of these factors allows the shader to accurately simulate true reflection, shadows, and refraction

References #

• Lambert’s cosine law as shading method for diffuse surfaces
• Phong Lighting as a more sophisticated method

Improved model #

• Includes Microfacets (Originally from models of light reflection for computer synthesized pictures )

• Regarding ray tree:

  For the case of surfaces aligned in such a way that a branch of the tree has infinite depth, the branch is truncated at the point where it exceeds the allotted storage

• Explicitly send rays at each ray hit point to the light sources to detemine if the point is in shadow by this light source

Unlike previous ray tracing algorithms, the visibility calculations do not end when the nearest intersection of a ray with objects in the scene is found. Instead, each visible intersection of a ray with a surface produces more rays in the R direction, the P direction, and in the direction of each light source. The intersection process is repeated for each ray until none of the new rays intersects any object.

The visible surface algorithm also contains the mech- anism to perform anti-aliasing. Since aliasing is the result of undersampling during the display process, the most straightforward cure is to low-pass filter the entire image before sampling for display.

Image #

@online{NvidiaWhittedRaytracerImage,
  author = {J. Turner Whitted},
  title = {A Ray-Tracing Pioneer Explains How He Stumbled into Global Illumination},
  year = 2018,
  url = {https://blogs.nvidia.com/blog/2018/08/01/ray-tracing-global-illumination-turner-whitted/},
  urldate = {2023-01-21}
}