Fire light emission cut off producing banding artifacts

[PIXELBOX_SRO]

Hello guys,

as the topic says pretty much.
Have a look at the ceiling.
If i set the cutoff to 0, banding is gone.



i understand the light cutoff paramedter but in interior environments it better set to 0 with this behaviour.
Just my 2 cents

Martin

[Svetlin.Nikolov]

Hey,

That's right. Did the render time change too dramatically between 0.001 and 0 though? This was the main concern when we left it at 0.001 by default.

Cheers!

[PIXELBOX_SRO]

I will make a test for u

[vlado]

@svetlin - the correct thing we need to do (for the v-ray lights as well, when I get to it) is outside the threshold to just sample the lights probabilistically...

Best regards,
Vlado

[Svetlin.Nikolov]

Well, currently Phoenix samples them probabilistically inside the threshold and does not sample them at all when the intensity is under the threshold. This is another aspect of the problem with managing the emissive lights inside Phoenix. Ultimately, a new V-Ray light would be the solution.

[LarsSonparsson]

Sorry to hijack the thread, but I think I'm having the same problem.
I'm not getting banding, but a lot of noise / fireflies in reflections.

In that attached render, Phoenix Light Cut-off is 0.002. If I lower it to zero, I get only noise in reflections.
If I set it to like 0.01, Reflections are clean, but the light banding is visible.

[Svetlin.Nikolov]

Yup, this is exactly the weak point of the emissive lights as they are right now - reflections, especially glossy ones, would be very noisy, because Phoenix is trying to handle V-Ray's job on its own.

[LarsSonparsson]

Ok thanks, good to hear that you already know where the problem is.

Keep us updated when you find a solution.

[Svetlin.Nikolov]

Roger that - this is one of the areas that would need the most attention.

[jstrob]

With my tank firing scene I emit and reflect light on the ground and it's really noisy and full of fireflies. Is there any workaround you could suggest while you find a solution?

I tried using only GI (emit light off) and it's the same. Maybe increasing subdiv of the emit light? Direct and GI I guess?

i notice the lighting, specular and GI passes are looking good, but the reflection one is noisy.

[jstrob]

Hey guys I found the solution!

It's just the settings I used all the time to avoid fireflies in glossy reflection even without Phoenix (I just forgot to use them in this scene):
In the V-Ray color mapping I just check on Sub-pixel mapping and I clamp the output to 5 or 8.

I'm pretty sure it will work for you too Lasse. It happen all the time when there are very bright sources being reflected, be it from an HDR environnement or light or PhoenixFD fire. Explosions are very bright sources that's why.
before:



after:



Both settings are needed cause here is what happen when you use only one:
Subpixel mapping only:

[jstrob]

And clamp only:


I also tried lowering the max ray intensity setting in the Global switches cause in the docs they say: "Its effect is similar to the Subpixel mapping + Clamp output options of the Color mapping section, but the Max ray intensity is applied to all secondary (GI/reflection/refraction) rays, as opposed to the final image samples. This allows fireflies to be effectively suppressed but without losing too much HDR information in the final image."

But even lowering it to 0.001 )no subpixel and no clamp) does not work in this case, I am loosing all light on the tank and still got all the fireflies.

[PIXELBOX_SRO]

Hey Jstrob
have you tried comparing the overal look of the frame when enabling subpixel mapping?
In my tests, enablin subpixel always changes brightness of the scene in some parts.
But perhaps the very high clamp value goes against that and levels out the differences???

[jstrob]

I almost always use it and I never noticed a change in the overall look, just a change in the highlights which become less bright. But you can make them brighter by rendering all the needed raw elements and adjusting in comp.

[LarsSonparsson]

Any updates for this issue?

I'm currently working with the scene where I need to get reflections and Phoenix lighting working.
I'm still doing simulation tests, but after a week or so, I should start to render passes out for comp.
Clamp and sub-pixel mapping might help, but I wouldn't like to go that way yet.