When you look at fur, the light has taken an extended journey before hitting your eye, bouncing around lots of fur fibers and their microscopic structures. You can imagine that it’s quite difficult for filmmakers to render these structures in CGI.
Researchers at the Universities of California in San Diego and Berkeley have devised an improvement over fur rendering that they think is both more efficient and more practical. It’s ten times faster than previous methods, and incorporates a more realistic model of fur to create more realistic images.
“Our earlier fur reflectance models on which this builds have been adopted,” Ravi Ramamoorthi, the study’s first author, told Gizmodo. “We expect this to be applied in practice very soon.”
Essentially, the authors write, folks normally depict hair as lots of cylinders that the light bounces around. But hairs are rougher than this—and accounting for the roughness can be too difficult from far away. And you can’t just model thousands of individual hairs. To try and capture this complexity, the authors treat each hair as nested cylinders through which light travels differently, scatters, and exits. This is called subsurface scattering, like the glow of light bouncing around a t-shirt covering a flashlight.
Animators already know how to render subsurface scattering—there are mathematical parameters that define how light behaves in these situations. Here, the researchers studied fur and converted the mathematics of the light bouncing around to a subsurface scattering model using a rather simple neural network, explained Ramamoorthi. They even validated their models using fibers collected from taxidermy stores.
The older fur reflectance models have been used in movies like Rise of the Planet of the Apes—but these newer ones aren’t just better, they’re ten times faster than the older method, he said. The team presented their findings at the SIGGRAPH Asia conference in Thailand back in late 2017.
This isn’t the end of the line for the research. “Within computer graphics, a long-time holy grail is to create photograph-quality realism,” he said. “Part of that is realistic characters, and fur is part of creating realistic animal characters.”