Post-Production – UV AOV

Even though I had achieved a fairly photorealistic standard in compositing the robots using Nuke, I still felt that they didn’t quite blend seamlessly into the scene. There was something about the metallic parts of the robots that felt unrealistic. To address this issue, I decided to add dirt and grime to those areas. Instead of retexturing, I opted to use a UV pass AOV, which would allow me to accomplish this in the compositing stage without having to repeatedly render the Maya scene.

Adding a custom AOV for this purpose in Maya is relatively straightforward. It requires a utility texture set to “flat” and a UV pass, which can be accurately read in Nuke. Essentially, it functions as an ST map, where each pixel corresponds to a position on the geometry relative to the geometry itself, rather than the world. This means that any applied dirt or grime moves and distorts with the geometry. With the use of high-quality square textures, a few cryptomattes, and correct blending techniques, I can effectively add dirt and grime to the robots.

Below is a time-lapse of the process I used to do this.