Added noise/lowering light subdiv when rendering animation using prepass.

[Tore S]

Hello,

I'm rendering an interior office scene and I'm having trouble with Vray Light sampling subdivs.

We are using Max 2020 and Vray 3.70.01

I have tried to optimize my scene by using higher sampling in my lights to get vray to ease up on the AA. When rendering the animation I use IR and LC in the normal way you would (calculate LC, use the LC when calculating the IR and finally render using the IR).
I have 4 images for reference, 2 are from a single frame rendered on my pc using IR and LC set to a single frame, diffuse and sample rate channels. The other two I have a screenshot from one of our render nodes rendering the image using IR prepass files.
As you can see in the photos the image that is rendered using prepass and backburner has a lot more noise and the AA sample rate is through the roof.

I have never encountered a problem like this, I have added screenshots of my settings as there is possibly something I have overlooked or mistakes I have done in the process.
I tried to import the whole scene into a new scene to see what would happen, but the results were largely the same.

Can anyone help me identify why this is happening and how to fix it when using prepass.

I rendered a sequence yesterday with the GI set to single frame, so every frame rendered it's own IR and LC (this had a lot of flickering as you can imagine), but the average render time was 11 min, I tried to do the same with the same setting, but using prepass, estimated 10h per frame....

I couldn't find someone with a similar problem while searching if someone has encountered this and found a way to fix it I would be grateful if you could send me in the right direction.

Thanks.

Edit: I mistakenly posted this in the wrong place, would it be possible for a moderator to move it to the issues section?

[Tore S]

As a test I tried to use 'store with irradiance map' on the lights, this removed the noise that was added, but it introduced some major artifacts, so that is not an option.

[Vizioen]

How long does it take for one frame using the recommended settings (BF + LC)?

[^Lele^]

The problem with toggling "use local subdivs" is that it will do so across *all* V-Ray nodes where subdivs make sense.
That includes shaders, textures (f.e. Dirt) and so on.
That makes figuring out what is happening a *very* strenuous job, much more so without having a scene in hand.

The bubbling of animated IM+LC is wholly expected, and it's why those methods originally had to resort to path-driven, sequence-distributed sampling.

My -personal- suggestion would be to reset the V-Ray settings to default, and render the sequence as BF+LC (as Ashley suggests above.) with the suggested settings (3k LC subdivs, retrace of 8.0).
Any render time over that of an IM will be well spent in a solution which won't bubble, and a single rendering of the sequence, as opposed to the endless fiddling with IM settings.

[Tore S]

thank you for the suggestion, I finally found a workable solution a few hours ago, switching adaptive lighting to full light evaluation 'enabled' the correct sampling on my lights. I assume the problem comes from the adaptive lights, from what I could find out it gets its settings from the light cache, so I'm guessing there was a problem there when I only use the LC when calculating the IR, and only use the IR when I render. This seems very much like a bug, I wasn't able to fix the bug specifically, but everything is rendering and that is good enough for me now.

As a side note, I think 'Store in Irradiance Map' would also work, the artifacts I got the first time around was from the Light cache, and that problem also came with full light evaluation, the problem was fixed by upping the Retrace option in LC from 2 to 8.

It has been hard troubleshooting all these problems since it only happens when I use backburner to render a sequence.

Thanks for the suggestions.