This is incredibly complex, especially for things like hair or skin – where the light is partially shining through the surface. Weta's approach to shading is to look to real-world physics. The shading models for different surfaces are based on the actual physical properties of those surfaces. Our in-house renderers, Manuka and Gazebo, use real-world physics to calculate how light interacts with each surface – down to the level of calculating wavelengths of light separately.