That Hair

"Subsurface scattering (or SSS) is a mechanism of light transport in which light penetrates the surface of a translucent object, is scattered by interacting with the material, and exits the surface at a different point. The light will generally penetrate the surface and be reflected a number of times at irregular angles inside the material, before passing back out of the material at an angle other than the angle it would have if it had been reflected directly off the surface. Subsurface scattering is important in 3D computer graphics, being necessary for the realistic rendering of materials such as marble, skin, and milk."

 

Picture: Direct surface scattering (left), plus subsurface scattering (middle), create the final image on the right.

 

This was used to spectacular effect in the Disney movie Tangled. And how about that hair?

 

"Many of the techniques and tools that were required to give the film the quality demanded did not exist when the project was started, and Disney Animation Studios had to create them on their own...

 

...Existing CGI technology continued to present difficulties: in particular, animating hair turned out to be a challenge. Senior software engineer Kelly Ward spent six years writing programs to make it move the way they wanted. As late as January 2010, the directors were still not sure if the Rapunzel character's length of hair was going to work. These problems were finally solved in March. An improved version of a hair simulation program named Dynamic Wires, originally developed for Bolt, was eventually used. To make hair float believably in water, and to surmount other similar challenges, discrete differential geometry was used to produce the desired effects, freeing the animators from executing these specific tasks directly, which would have taken days instead of minutes."

 

 

There are solid reasons why this was the most expensive animated film of all time. You could design and build a ship with the amount of time and expertise (oh, and 260 million dollars) thrown at this project.