“Rendering translucent robots”

One of the greatest difficulties of I, Robot, was designing the rendering pipeline for the robotsí translucent plastic shell. We needed to see the inner mechanics blurred by the material of the shell. The plastic material also needed to exhibit light scattering properties. In addition, we needed to render a large number of hero robots quickly. We decided to rely on Rendermanís ability to output multiple render passes simultaneously through arbitrary output variables (AOV), and then achieve the translucent effects through composting. Compositing was computationally faster, and allowed us to make quick changes to meet the directorís desired appearance.