So I started experimenting with this since I am working on a project that involves a lot of volumetric lighting and thus has a really bad problem with noise, and thus requires a disproportionate amount of sampling. So I managed to get this:
I used 1200 samples and rendered it at 1920x1080. After rendering it, I put it into Resolve and applied some noise reduction. Of particular note is the area surrounding the light which was(and still is to a degree) a bit noisy. The original render was still a bit rough, so I used a power window on it to use some really strong noise reduction that I didn’t want used anywhere other than where it was absolutely needed. I also applied a little bit of color grading for aesthetic reasons. Anyway, I rendered the same frame out at 3840x2160 and applied all the same effects in post, with the only difference being that I downressed it to HD after everything else, and this was the result:
You might notice that for some reason the downressed version is a bit darker and a bit less contrasty than the HD one, this is not a result of the post effects I did, but carries through from the original render. I can somewhat mitigate it by color correcting to match, so it’s not a huge deal. In the end he verdict is that the 1200 sample image took two hours and fifteen minutes, the 300 sample image took two hours and six minutes. So there was a nine minute difference in render time which is a six percent time savings. Add in the extra second per frame it took me to render out the downressed and denoised plate, and we are looking at a definite improve, though nothing dramatic, it does add up.
As a side note, I was actually quite happy with the results from using Resolve’s noise reduction capabilities and am wondering if I can use it to knock more time off of my renders.