Wild GI flicker

[BBB3]

Hey,
I'm rendering an animation of a tough (i.e. relatively dimly lit) interior scene directly from within Vantage using an imported animated camera and getting really wild GI flicker.
I'm saying GI flicker because it is only happening on those parts of the image that are just lit by GI and don't receive any direct light. It also stops if I uncheck the light cache (but that's not an option because that creates a shed ton of noise).
So what's the best practice in these situations where you absolutely need GI?
(can't upload the footage here because it exceeds the size limit but I can't send a download link if anyone wants to check it out)

[vladimir.nedev]

Yes, please, send us the footage.
It will be even better if you can send us the scene, as we will be researching some improvements to our GI sampling and it will be a useful test scene.

Greetings,
Vladimir Nedev

[npg]

Have you tried increasing the light cache sample limit? Try a different cell size as well.
Is your secondary ray clamp value set to the new default (200) we introduced in 1.8.3? This lets more light in.

[BBB3]

Yes, please, send us the footage.
It will be even better if you can send us the scene

Sending the scene and the footage now to your email, Vladimir. Appreciate you taking a look.

[BBB3]

Have you tried increasing the light cache sample limit? Try a different cell size as well.
Is your secondary ray clamp value set to the new default (200) we introduced in 1.8.3? This lets more light in.

Hey Nikola. Sorry for the stupid question but should the cell size be bigger or smaller? And yes, the ray clamp value was set at 200.

EDIT: Yes, I did raise the sample limit a few times by 256 increments but it didn't really make a difference.

[vladimir.nedev]

Sending the scene and the footage now to your email, Vladimir. Appreciate you taking a look.

Thank you, can you also send me the "HBFullS.exr" environment or tell me where to download it from ?

Greetings,
Vladimir Nedev

[npg]

I think a larger cell with a higher limit (thousands) should produce a smoother and more stable result, but I haven't made many experiments in practice.

[BBB3]

Thank you, can you also send me the "HBFullS.exr" environment or tell me where to download it from ?

Sorry, forgot to pack the maps. Doing this now.

[BBB3]

I think a larger cell with a higher limit (thousands) should produce a smoother and more stable result, but I haven't made many experiments in practice.

Nope. Unfortunately it isn't making any difference. Still flashing away like there's an electric storm in that kitchen...

[BBB3]

Thank you, can you also send me the "HBFullS.exr" environment or tell me where to download it from ?

Maps on their way. I'm using the last camera in the list by the way for this sequence.

[vladimir.nedev]

Maps on their way. I'm using the last camera in the list by the way for this sequence.

Тhanks for the textures.
Can you show us the exact sequence render options that you used to render the animation ?

Greetings,
Vladimir Nedev

[BBB3]

Unfortunately not. I've overwritten them many times while troubleshooting. But from memory the video I sent you was pretty much rendered with the default option, except Samples, which I think I set at 700. I also made the denoiser final pass-only. No auto exposure and motion blur on.

EDIT: Bumping cell size and limit a lot seems to help with the GI flickering, but it also appears to be making the image noisier, which then introduces some denoiser flickering...

[vladimir.nedev]

Unfortunately not. I've overwritten them many times while troubleshooting. But from memory the video I sent you was pretty much rendered with the default option, except Samples, which I think I set at 700. I also made the denoiser final pass-only. No auto exposure and motion blur on.

Thanks, I think most of the flickering is caused by our (Vantage's) subpar (compared to V-Ray) handling of reflective caustics.
So they introduce very bright samples in the light cache.
I have to do more testing however.
Hopefully we can fix this in the coming week(s) and give you a build to test.

In my renders I am noticing an issue in the tile reflections, which is not present in your clip.
Might be a regression in our internal builds.
Which Vantage build are you using ?

Greetings,
Vladimir Nedev

[BBB3]

Hey Vladimir. I'm using Version: 1.8.3, Build: 1519081, Oct 25 2022

That's an interesting theory. Both the tiles and the countertop are very reflective. Would that make them the culprit? I guess I could try the animation by making them diffuse and see if it changes anything...
I obviously don't know what I'm talking about, but would it make sense for the GI to be calculated from a very simplified version of the scene, with only diffuse objects with low-res textures? Kind of like Lumen is computed from a dummy version of the scene in UE5. This would make the GI lower quality but hopefully more stable across frames. But like I said, I'm sure you guys have already thought of this.

EDIT: I can confirm that when reflections are disabled on the countertop and the tiles (fully diffuse materials), the flickering is hugely reduced, even with lower limits on the LC. So I think you're right.