Excessive noise/fireflies with Falloff as Glossiness

[Joelaff]

Curious how much additional Light Cache samples help in this sort of scene. With Path Guiding?

Also, what sort of effect will the new Adaptivity Clamp have on this? Would it make it worse because it would reduce the number of samples in the bright highlights? Need to get a pause so I can install the latest update.

We usually end up adjusting a second HDRI for just the reflections, and either blur the sun, or reduce it's intensity. This can sometimes have deleterious effects on the look-- very case by case. I know Olli has tried all this before.

[^Lele^]

Curious how much additional Light Cache samples help in this sort of scene. With Path Guiding?

Pgl helps nothing at all for this case.
I think it's because this is a direct reflection from a dome, albeit with those characteristics of occasional high intensity.
PGL has been seen helping the very difficult, many-bounce stuff, like thin volumes, tertiary speculars, and so on.
I'll profile the render and talk to the Dev to see if anything can be done.

Also, what sort of effect will the new Adaptivity Clamp have on this? Would it make it worse because it would reduce the number of samples in the bright highlights? Need to get a pause so I can install the latest update.

Considering the reflection is entirely in the visible range, adaptivity clamping wouldn't help here as it wouldn't be called into action.
I am left wondering if Olli could get to a similar look using sheen + GGX, and if that was the case, if it required less or more sampling to converge porperly.
I may give it a gander myself.

We usually end up adjusting a second HDRI for just the reflections, and either blur the sun, or reduce it's intensity. This can sometimes have deleterious effects on the look-- very case by case. I know Olli has tried all this before.

Indeed, this is what i referred to in my earlier post mentioning trying to reach a compromise.
It's sadly not always possible, and I personally would have been pretty happy to know it eventually converged properly with whatever look, if with a ton of brute force, when in production, as That I could budget for.

[Joelaff]

Interesting idea about sheen. Gotta say I don't use it a whole lot, except for velvet and dust. Should probably do more experiments there. I often find myself lowered the GGX tail down to even as low as 1.3 It looks really beautiful. Have not run into fireflies that I could specifically attribute to that, but perhaps because I did not know to look there.

The single biggest firefly fix for non-HDRI I have found is to duplicate the lights and reduce the directionality of the copy using the copy for the reflections. Highly directional lights (like > ~0.5, but especially up in the 0.9 + range) cause no end of firefly troubles.

[^Lele^]

It looks really beautiful.

I also think it's an awesome BRDF.
Even without energy preservation at low gloss, i was having fun making it look diffuse, but not quite. Just something else compared to the others around.
I mean, the retro-reflectivity at low gloss and tail is truly a joy for the eyes.

[fixeighted]

As a mental excercise, say we have 50 samples that average to 0.03f and then one comes in at 150000.0f (we hit the sun disk!).
If we discarded the sample as "bad", we'd get no sun reflection whatsoever, but to properly sample the reflection, we'd need 50 times the 50+1 samples to try and get 50 sun disk samples.
As we deal with statistics, it's not even guaranteed that we'd get those fifty bright samples if we sampled fifty times more.

I won't pretend to understand fully this issue, but what if there was a boolean argument (if that is the correct terminology) to arbitrarily clamp or otherwise deal with the random e.g. 150000.0f instance when it occurs?
I'm guessing that this has maybe been thought about, but it's intersesting and too much wine says I should ask

[Joelaff]

As Lele mentioned above you can't just ignore or clamp the superbright, because it is what is actually illuminating the pixel. So you need its contribution. I may be better to trace from the light first to gather some prior knowledge to apply to the from the camera rays. Bidirectional Path Tracing (BDPT) or Metropolis Light Transport (MLT), but both will take more time.

[kosso_olli]

Olli seems to have to deal daily with nightmare production cases: he can't quite cheat it, the sizes are ginormous, people can see the dust specks.
I'd be twice my age if i had to do the same on a daily basis.

You should see me these days, I do look twice my age!

Thanks for everyone involved for the tips and ideas, it helps a lot.
Right now, raising the Max AA considerably is the easiest way. My biggest fear was to rebuild the already approved shader for all the shots...

Sheen might be worth a shot, though. Will try that!