This image shows the effect of global illumination on hair. Color bleeding can be seen on either side of the hair model, and the overall illumination of hair makes it fit to its environment.

Abstract
Both hair rendering and global illumination are known to be computationally expensive, and for this reason we see very few examples using global illumination techniques in hair rendering. However, hair rendering using only direct illumination in scenes rendered by global illumination methods creates inconsistencies in the overall appearance. The goal of this project is to achieve practical hair rendering with global illumination using techniques specialized for hair, and propose solutions for hair rendering with global illumination to make it affordable for industrial applications. Both ray tracing and projection based alternative solutions are explored, considering and categorizing different light paths that lead to a complete global illumination solution. The preliminary results of this project were presented in SIGGRAPH2005 as a sketch, and SIGGRAPH2006 as a poster.

No global illumination on hair	No hair self-shadowing

The image on the left is rendered without any global illumination on hair. Notice how the illumination of hair contradicts with the rest of the scene. The image on the right is rendered using global illumination, but not including hair strands in global illumination computation, thus ignoring self-shadowing between hair strands.

This is a close-up image of the same Cornell Box scene with a full global illumination solution including inter-reflections between hair strands.

Here is a hairy teapot illuminated by a uniform skylight.

		Cem Yuksel, Ergun Akleman, and John Keyser Practical Global Illumination for Hair Rendering Pacific Graphics 2007, to appear [Preprint PDF] [BibTeX]
		Cem Yuksel and Ergun Akleman Rendering hair with global illumination ACM SIGGRAPH 2006 Research Posters, 2006 [BibTeX]
		Cem Yuksel and Ergun Akleman Rendering hair-like objects with indirect illumination ACM SIGGRAPH 2005 Sketches, 2005 [BibTeX]