If light penetrates a material, it is changed. This can be observed by holding one’s hand against the sun. The edges of the fingers look red, because the light enters the skin and is then scattered. “This is called subsurface scattering (SSS) or volume scattering”, explained Christian Freude of the Institute for Computer Graphics and Algorithms at the Vienna University of Technology. The rendering of faces is particularly complicated.
It is in fact possible to precisely calculate light scattering, but this is a complicated process. Researchers at the Vienna University of Technology, the University of Zaragoza in Spain and the software company Activision-Blizzard have now decisively shortened the process. “At first one calculates the scattering of a single beam of light below the surface. With this result a simple filter profile can be created, which can then be applied to the images again and again”, Freude stated. Thus the computer image is created with conventional methods, and is then modified using the Separable Subsurface Scattering (SSSS) technique. A normal computer needs less than a millisecond for this process. The smoothness of the motion is not affected.
Activision-Blizzard is already using this method. The research team is confident that the SSSS method will be used in many other applications in the future. The new method was presented in the scientific journal “Computer Graphics Forum” so that other users can make use of the new approach.