By Conard Holton
At the SIGGRAPH conference this year, Henrik Wann Jensen, a computer science professor at UC San Diego (San Diego, CA, USA), presented a computer graphics model capable of generating realistic milk images based on fat and protein content. "If you tell the new computer graphics model how much fat and protein you want in your milk, the model generates the information to create a life-like milk image by determining how light will interact with a specified ratio of milk fats and proteins," says Jensen.
In addition to creating images based on what the material is made of, the author showed that the model can work backward and determine how much fat and protein a sample of milk contains, based on just a digital picture of the milk. "Putting the model in reverse, grocery stores could identify spoiled meats, contaminants, or other food-safety issues--if a particular food problem consistently and detectably changed the light-scattering properties of the food," says Jensen. The model generates realistic graphics of materials that absorb some light and are not made of perfect spheres.
The paper extends the Lorenz-Mie theory, which is a complete solution to Maxwell's equation for scattering of electromagnetic waves by a homogenous, spherical particle embedded in a non-absorbing medium. Jensen's model eliminates the restrictions of the Lorenz-Mie theory for media such as milk, in which the embedded particles (primarily proteins, fat, and vitamin B2) are not perfect spheres, and the host medium (water) absorbs light. "If you are trying to generate realistic computer graphics, it is intuitive to specify what the material is made of, such as the amount of fat and protein in the milk. In the past, this required determining how the milk would scatter and absorb light," says Jensen.
Jensen is now extending the model so that it can predict the appearance of skin based on a detailed description of dermal structures other than hemoglobin and melanin. Understanding how structures within the skin scatter and absorb light could be important to doctors who are using light to treat skin cancer and other skin diseases.
