BF/LC Flicker

[Morne]

Hi all

I have an animation with moving objects rendered with BF/LC (mostly universal). I'm getting some huge flicker however from GI (all other channels do not flicker).
Here's my LC settings:


When I say huge flicker, I mean big areas flicker. Looks like about 1 meter diameter splotches, although its not splotches, more colour variance.

I have secondary rays bias on 0.001 also because there are some VERY SMALL parts that do have overlapping faces due to the corners from sweeps. BUT, the areas that flicker has nothing to do with the overlapping geometry because the flicker is HUGE and also its nowhere near the coplaner areas. The coplaner areas on the sweep are so small, in on a 720p frame its probably only a 50th of a pixel big, if that. And the overlapping areas DONT flicker

Any thoughts?

(Sorry can't show screengrabs, video examples or stripped scene)

[Morne]

OK that is weird. I tried BF/BF on 1 frame and it actually shaved off a few seconds on the render. Wasn't that suppose to be slower than BF/LC?

Will render a few frames and see how it goes. That particular one may have been a fluke

[Morne]

OK tried a frame a bit further along, and that one with BF/BF is taking 5 TIMES LONGER than BF/LC

So I have to sort the LC issue it seems

[vlado]

You will need more subdivs for the light cache, and also retrace of 0.5 might be too low and may cause flickering near corners - try 1.0 (the default) instead.

Best regards,
Vlado

[Morne]

You will need more subdivs for the light cache, and also retrace of 0.5 might be too low and may cause flickering near corners - try 1.0 (the default) instead.

Best regards,
Vlado

Thanks Vlado,
I'm rendering 720p and I used the formula:
(square root [ 1280 X 720 ]) to get to the light cache subdivs value. What would you say is a better value for this? Maybe 2000?
And what is the correlation between this and the sample size?
Currently the sample size is 0.02, should I maybe drop that lower?

[svetlozar.draganov]

Sample Size parameter determines how large will be the individual light-cache samples, Subdivs parameter determines how many camera paths will be fired into these samples.
In other words Sample Size will tell Vray to how many pieces the scene will be subdivided and Subdivs will determine the accuracy of the color of each piece.
Lower values for Sample Size will generate more detailed GI solution but if the Subdivs parameter is also very low the boundaries between the separate samples will be very well visible and in order to fix that you have to increase Subdivs parameter.

The right value for Subdivs parameter depends from the scene complexity but in general values under 1000 are not suitable for animations. Try to double that value and run another test. You can also try to decrease the Sample Size parameter although the default value usually works fine in most of the cases.

Please check the following page for more information on that matter:
http://docs.chaosgroup.com/display/VRAY3/Light+Cache

[Morne]

Yes I'm running a quick test with 2400 subdivs. So far a 20 min frame has increased to 25 min a frame just by upping the subdivs. Will report back in a little while if this helped...

It's a bit of a catch 22. In general, things look ok(ish), but there is a lot of BF and reflection noise (just noise, not flicker). I'm hoping to smooth this out a little more in post. Unfortunately there's no budget for frames taking anything longer than 30min a frame so I have to do what I can to balance render time vs quality. I may decrease reflection a bit in an attempt to make the fine noise less obvious.

[Morne]

Jip, 2400 subdivs did the trick. No more LC flicker

Now to clean the noise a little more...

[svetlozar.draganov]

Glad to hear that the issue is resolved.