An ambient light illumination model

@inproceedings{zhukov1998ambient,
  title={An ambient light illumination model},
  author={Zhukov, Sergey and Iones, Andrei and Kronin, Grigorij},
  booktitle={Eurographics Workshop on Rendering Techniques},
  pages={45--55},
  year={1998},
  organization={Springer}
}

The original paper that introduces Ambient Occlusion (???), after work from (Miller 1994).

Apply the Rendering Equation to ambient occlusion, setting some assumptions to simplify it

1. all light comes from an infinite uniform environment light, which might be occluded by the geometry around x;
2. all surfaces around x are purely absorbing (i.e. do not reflect any light), and
3. the surface at x is diffuse.

Transforming the Rendering Equation into:

• is the diffuse BRDF with albedo
• is the Visibility Function
• clamped(0->1) cosine of the angle between surface normal at and the view direction used for Area Foreshortening