When using path tracing, rough surfaces look good using very few samples. Even while moving the camera the surface is clearly rough, even though the renderer hardly accumulates frames.
As I understand it, roughness is a measure for how randomly light rays “bounce” when making contact with a surface. Intuitively, when light bounces very randomly, you would need many samples to converge to a realistic color.
As a comparison I created a material with a roughness close to 0, but using a very fine-grained noisy normal map. This material did indeed require many samples to start looking rough.
My questions are:
- How does UE achieve roughness using only very few samples?
- Is there a fundamental difference between using roughness and using a noisy, extremely fine-grained normal map?