Progressive sampler doesn't produce same level of noise in the same amount of time

[Alex_M]

I'm having some issues with the progressive sampler. If I set it to render for let's say 25 seconds with Noise Threshold 0.0, it produces substantially cleaner image in this amount of time compared to running it indefinitely and using the Noise Threshold parameter set in such a way that it terminates after 25 seconds. Am I missing something? Here's a screenshot:

[im.thatoneguy]

.15 is way too high. So it's probably quit working entirely on the "noisy" sections (which it considers clean) and has moved on to the really really noisy stuff like GI caustics. If you look at the water you can see there are a few fireflies on the 0.0 because every pixel is being sampled equally. However since your noise threshold is so high it's considering the noisy side of the boat "Done" and focusing on the handful of GI caustic pixels (which are absent in your "noisy" image).

I wouldn't go above 0.02 unless you have good reason.

Just as a note I believe Vray samples its noise in linear space so .15 ^ (1/2.2 gamma) = 40% gray. That's a pretty easy threshold to pass. It's helpful to use the "show samples" option or renderelement to see exactly how your pixels are being sampled.

[Alex_M]

But if I set the threshold to 0.02 the render takes ages (~5 min) to get as clean of a result as setting it to run for 25 sec with Noise Threshold 0.0. Can you let me know how should I set it up so that it clears the noise in ~25 sec by using only the Noise Threshold value? If it can clear the noise in 25 sec. by using only the time parameter, it should also be able to clean it in this amount of time by using only the threshold parameter, no?

[re:FORM]

Try lowering your max samples to 24 or 32, I found 100 causes too many samples being lost to noisy elements that don't actually need that many samples to look good.