Metal Surfaces "Chattering" (video included)

[YOUNG_LEE]

Hi,

I'm rendering a complex indoor scene in 3.xx and I can't seem to get rid of some sparkling/chattering on some metallic surfaces. See vimeo file (full screen + HD to see the problem). Problem areas are circled in red. My metal shaders have 80 subdivs samples. Render settings attached.

Any help would be appreciated, thanks!!

https://vimeo.com/178072513

[Neilg]

First thing i'd think is to do a 5 frame small region and raise the minimum subdivisions from 1 to 4 ish. do you have the passes rendered to see if it's in the reflection, and what the sampler is doing in that area?

[YOUNG_LEE]

I'm doing a test render now with aforementioned passes. I raised minimum subdivs to 2, since 4 would kill my rendertime. will update in a few days, thanks

[vlado]

It would be good to take a look at the render elements first to see which component is causing the flicker and increase the subdivs for that component.

Best regards,
Vlado

[YOUNG_LEE]

So upping the min samples to 2 didn't seem to have any effect. After viewing the sample rate and raw reflection, it does seem that the problem lies within the subdiv samples of certain surfaces. The metal shaders in question already have subdiv values of 80 however, which seems rather high already. Could the chattering be coming from reflections of a another surface in the scene?

Here is a video with three different passes:

[t.petrov]

You just have noise in the image and you have to find a way to minimize it.
There is no point rising the max subdivs, because your samplerate render element is mostly blue - this means that most of the image is sampled closed to the minimum subdivs.
For your case probably it will be better to lower the noise threshold.

Is there any particular reason you want to enable "Use local subdivs"?
Have you tried setting it off and using larger min shading rate?

[YOUNG_LEE]

"Use local subdivs" is checked on because I figured it was good optimization procedure to tweak individual shaders subdivs. Am I misunderstanding this? I'll try rendering with your suggestion and update in a few days, thanks

[t.petrov]

These days it is the opposite - most of the times V-Ray is better at deciding what to sample more, so we advise people to leave the default and only play with min, max, noise threshold and min_sample_rate.