GI flickering with BF+LC

[seq]

Hi together,

a never ending story: Rendering an animation with GI.

For our current project we need to render several scenes with a moving camera, moving objects and changing of the light conditions (e.g. night scene where the lights turned on or daytime scene where the blinds get closed).

We thought that with BF + LC we are on the save side concerning GI flickering.

Our settings are:

Image Sampler: Adaptive DMC, Gaussian with 2
Adaptive DMC: 1 / 10 / 0.009

Brute Force: 16 / 3

Light Cache
16 / 1400 / 0.02
Store Direct Light off, Scene Scale, Adaptive sampling, Use camera path on
Filter type: None
Prefilter: 100
Use LC for glossy rays enabled
Depth: 100
Single Frame

DMC Sampler
Adaptive Amount: 1
Adaptive Threshold: 0.002
Min. Samples: 6
Subdiv. Mult: 1.5

Rendered via batchfile with DR.

Overnight we rendered a scene where the light conditions did not change. And we get this:

http://upload.sequenz.com/seq_100415_GI_flickering.mov

http://upload.sequenz.com/seq_100415_GI_flickering.wmv

Only 4 images of the sequence. Please use the arrow keys to see the GI flickering from the first frame to the second. The only light that is in the scene is VRaySun which shines throught the windows. The area the camera looks at get only indirect light. And that seems to be the problem.

To cut a long story short: Is there any way to render flicker free animations when the camera moves, the light conditions changes and in some scenes objects moves?

We thought that BF+LC are great for this, but I guess we would need to use BF+BF to get what we want, or?

Thanks and sorry for the long post.
Lars

[vlado]

What are your light cache settings (specifically the subdivs number)? It looks to be too low.

[edit] Just saw you posted them; try a number like 2000 to 3000 - it should get you a more stable solution.

You can also make a preview of the animation with the light cache as both primary and secondary engine to make sure it is ok.

Best regards,
Vlado

[seq]

Ah, this helps a lot! Thanks, Vlado.

Now the LC calculation takes about 4,5 minutes/frame. Which leads me to my next question: When we use DR with 5 machines all machines render the LC for its own for each frame. Isn't that a waste of time? Wouldn't it be faster when each machine renders a part of the scene or renders another scenes?

[vlado]

We are working on that, but for now it is one of those cases where rendering one frame per machine works better.

Best regards,
Vlado

[seq]

Okay. One last question: We write out vrscene files from Maya and render them via a batchrenderscript. For the LC we set the passes to 16 as three of our render machines have 16 cores (with HT). But one has only 8 and another one only 4 cores. Can we use the same vrscene file (with 16 passes) for all of the machines?

Thanks,
Lars

[vlado]

Yes, no problem about that.

Best regards,
Vlado

[seq]

Great.

Wish you a wonderfull sunny weekend.

[seq]

The VRayMtl2Sided material is/was the bad guy! We used that material for the curtains and in every scene where the curtains where inclosed, we get those horrible flickering. Even with 3000 subdivs for the LC. After replacing the material with a normal VRayMat the flickering went away.

[vlado]

Ok, thanks for the pointer; will look into it.

Best regards,
Vlado

[seq]

Update: It seems that if we add a texture to the opacity map or just lower the value (<1) on a VRayMtl, we get this flickering problem. The same is true for the VRayMtl2Sided.

So next thing we try out is to use the old school methode for our curtains, which will increase our rendertime quite a bit.

[vlado]

Is it possible to get a scene for this (you can send it to vlado@chaosgroup.com)? It will be very helpful to debug the issue.

Best regards,
Vlado

[seq]

I'll try to send you a scene tomorrow. We are still busy modifying the scenes, so that we get a flicker free result. We will render two test sequences over the night.

[seq]

Just send you a scene and QT.

[vlado]

Yes, thanks for the scene!

Best regards,
Vlado

[waaazoo]

Vlado, no news on that ? I had that problem too on a recent test.

regards,