GI Flickering, no matter what method is used.

[sebbiej]

Hi all,

I'm getting GI flickering on an interior scene that I can't seem to get rid of and urgently need advice, I've tried messaging Chaos Tech support 2 days ago but haven't had a response.

My (small kitchen) scene is lit via a HDRI, and this is the only light in the scene. I'm using V-Ray 6 Update 2 - v6.20.00 from Feb 11, rendering it via Deadline on a couple of PCs using V-Ray GPU. There is only a slow moving camera in my scene and no moving geometry.

I've tried using Light Cache with V-Ray's default animation - subdivs set to 3000 and as far as 9000 - it flickers on a few objects in particular places, not all over. This is with the mode set to Single Frame.
I've tried saving out the light cache via rendering a frame with Autosave switched on, then setting the mode to From File - it flickers, in the same places as before.
I've tried using Brute Force on it's default depth of 3 - it flickers. I've tried upping this to 8-10, it flickers in the same places.
I've tried Brute Force locally and on Chaos Cloud, it flickers in the same places.

I can't really render this on CPU as frames take over an hour on our PCs, compared to 7 minutes on our RTX4090, my deadline to render a 160 frame shot is short... I need it rendering over the weekend.

What else can I try to remove the flickering?

[stezza]

Can you post some render settings tabs so we can see more details including light settings.

[sebbiej]

Can you post some render settings tabs so we can see more details including light settings.

stezza here are my settings

[sebbiej]

One weird thing I have noticed with my scenes is that the Light Cache Preset mode automatically changes itself to Still from Animation everytime I save my scene on my PC then open it up on the render farm PC. I have to reset it to Animation before rendering. A bug, maybe?

[stezza]

First test I would do is use bucket with cpu
turn off "From File" to single frame
LC animation should be fine.
Try a few frames see how that goes.

Can you share a pic of your render result?

[sebbiej]

Sure, I'll give that a try. Only issue is that CPU is going to take way too long to render out the sequence, we need it done on GPU preferably.
I'll send you a PM stezza with the result I'm currently getting.

[SonyBoy]

One weird thing I have noticed with my scenes is that the Light Cache Preset mode automatically changes itself to Still from Animation everytime I save my scene on my PC then open it up on the render farm PC. I have to reset it to Animation before rendering. A bug, maybe?

This has been a bug for years, however although the drop down preset shows it's been reset to "Still" the number of subdivs below remains at 3000, which is the Animation preset value, and I believe the other attrs. stay at Animation settings too. It's annoying though.

[seq]

Have you found a solution? Perhaps adding some additional lights would help. To light an interior only with an HDRI is really a challenge for any render. That is why in real life photographer and film guys/girls need so many lights.

[sebbiej]

Have you found a solution? Perhaps adding some additional lights would help. To light an interior only with an HDRI is really a challenge for any render. That is why in real life photographer and film guys/girls need so many lights.

Yeah, I found a solution with some help from Stezza. So, the flickering was happening below a kitchen worktop on my scene on the top of the front of the kitchen cupboard doors. If I made the cupboard doors slightly intersect the worktop the flickering disappeared. I think as there was a small gap, V-Ray GI couldn't figure out what was meant to be happening there. I also swiched to bucket mode and that helped, although I'm not sure if it's that which made the difference, or not!

[seq]

Perfect. Then happy rendering!