I ran across this a couple years, don’t remember if I shared it!
Basically an algorithm that can take a noisy (rendered) image and make it quite smooth looking, even temporally (very little flickering in an animation). The interesting bit starts about 1 minute in. I’m sure it has drawbacks, but the results are quite impressive with only one ray-per-pixel.
Has any attention been given to this? It certainly is not perfect, but might make the Viewpoint preview a bit cleaner.
https://drive.google.com/file/d/0B6eg_ib7k4PoaVhWN3VYRHo0NDQ/view (actual video from paper)