Henrik Wann Jensen Associate Professor Computer Graphics Laboratory Computer Science and Engineering University of California, San Diego CSE 4116 (map) 9500 Gilman Drive La Jolla, CA 92093-0404 henrik-at-cs.ucsd.edu (The best way to reach me, note)

My area of interest is computer graphics with a focus on realistic image synthesis in particular appearance modeling, global illumination, and rendering natural phenomena. I am currently teaching Rendering Algorithms.

	Appearance modeling is an active area of research in computer graphics. Understanding the complex and diverse appearance of materials is essential for rendering compelling images. My primary research in appearance modeling has been in the area of subsurface scattering. I started looking at techniques for simulating volumetric subsurface scattering at MIT in 1998. Previous methods had only considered 1d transport wrapped into a BRDF model and therefore ignored the transport of light through the material. At MIT, we developed techniques based on photon mapping and path tracing to simulate the darkening of many wet materials as well as the translucency of weathered stone. Photon mapping is quite good at simulating subsurface scattering, but it becomes costly for highly scattering materials such as milk and skin. In the fall of 2000, we were investigating alternatives to the Monte Carlo methods, which resulted in the development of a new technique based on a diffusion approximation. The diffusion approximation is much faster than tracing individual photons, and it is simple enough that a BSSRDF can be formulated. The BSSRDF is particularly suited for highly scattering translucent materials where the assumptions in the ubiquitous BRDF approximation break down. As an example, the BSSRDF was used to render the translucent marble bust that is shown here. Note how the BSSRDF captures the the soft and smooth appearance as well as the light diffusing through the marble - something that a BRDF cannot simulate. The BSSRDF research has been adapted rapidly by the movie industry and it won an academy award in 2004. Lately, we have worked on techniques for rapid evaluation of the BSSRDF model, and extensions to simulate diffusion in multilayered translucent materials such as human skin. Recently, we developed a generalized Lorenz-Mie theory for computing the optical properties of translucent materials and scattering media.
	Global illumination is another active area of research that involves the simulation of all types of light scattering in a model. My PhD research addressed the simulation of global illumination including caustics by introducing the concept of photon mapping. The key features of the photon mapping algorithm are the use of photon tracing and the photon map. The photon map is decoupled from the scene geometry, and it can be used in models with millions of objects and complex materials. Photon mapping is a practical technique capable of simulating color bleeding, caustics, participating media, subsurface scattering, and motion blur. Today, photon mapping is implemented in most high-end rendering software, and it is being used in architectural simulations, computer games, and movies. As an example there was a nice caustics sequence (light focusing through a glass of whisky) in Final Fantasy. I have mostly been concerned with the caustics formed as light is focused through a glass of cognac.
	Rendering natural phenomena is a growing area of research in computer graphics. Examples include a physically based model of the night sky. The goal of this project was to simulate all important visual elements of the night sky (the moon, stars, the atmosphere, the Zodiacal light etc.) including their appearance to the eye (loss of color and blue shift). For this purpose we used multi-spectral rendering combined with an accurate simulation of light scattering in the atmosphere. Another project addresses the simulation and rendering of smoke and fire.