GI Flicker Tips Tweet

[Teddi]

Anyone have any tips on removing flicker from animation renders?

I've got a scene with 4 area lights, a metal table and a midi controller (which is the subject).

The controller has some shiny plastic knobs on it, they're made to look like reflective metal so I've used a silver material which looks correct.

However I've just rendered a slow dolly shot (moving sideways) and one of the reflective knobs is pulsing/flickering (getting brighter and darker), it's doing this in regularly timed pulse.

The other knob which is at a different angle and location is fine.

My render settings are..

Pathtracing Kernel

Samples: 1554
Diffuse: 4
Specular: 14
Ray Epsilon: 0.0001
Filter size: 1.2
Alpha shadows ticked
Caustic Blur: 1
G.I. Clamp: 1.08
Alpha Channel not ticked
Keep environment ticked
Path Term Power: 1
C Ratio: 0
Static Noise: not ticked
Parallel Samples: 16
Max Tile Samples: 16
Minimize Net Traffic: not ticked (not using network render)
Adaptive Sampling: not ticked
Noise Threshold: 0.03
Min. Samples: 256
Expected Exposure: 1
Group Pixels: 2x2

Any tips appreciated.

From previous experience if I rendered this with the PMC Kernel I think it would be fine, but that would quadruple my render times and I have a fairly tight deadline.

[bepeg4d]

Hi Teddi,
do you have bump or normal maps in the knob material?
If yes, try to reduce the power, you should have less flickering noise.
I would also enable Adaptive sampling with the following settings:
Sampling: start with 4000
Max tile : 32
---
Adaptive sampling: on
Noise Threshold: 0.05
Min. Samples: 512
Expected Exposure: the exact exposure that you have in Camera Imager node
Group Pixels: none, or 2x2

ciao beppe

[Teddi]

Thanks for this Beppe.

The silver material does have a bump map so I've unchecked that for now.

I also used the settings you suggested but the flicker is still there.

I just tried removing some things from the scene: the table and the four lights (which are area lights placed in front of Kino Flo light models, originally I used a blackbody emission texture on the Kino bulbs but that seemed to slow rendering times down and the lights are so bright you can't see the bulb detail anyway so I replaced them with simple area lights).

With the basic off-white studio and three large invisible area lights the flicker has gone.

So I'm guessing it's to do with what the knobs/silver material is reflecting.

Not sure what to try next.

Cheers.

[bepeg4d]

Hi Teddi,
you can try with the area lights invisible, and by addingbthe blackbody emission to the filament, but with Cast illumination disabled. In this way you can set the power to a lower value with nice reflactions and zero noise.
ciao beppe

[Teddi]

Thanks Beppe,

The tip with the lights was useful thanks.

After investigating further I think the flicker problem was actually more to do with resolution or aliasing.

I tried rendering the same scene with the PMC kernel and the same issue was apparent, I changed the metal material for something less reflective and the issue was still there too but less pronounced.

On shots which are further away or closer the issue disappears.

I think on this one particular shot the renderer couldn't resolve the detail cleanly, similar to aliasing or moire in a camera system.

The knob is knurled so the reflections contain a lot of detailed information which changes per frame as the camera moves.

If I'm right some sort of anti-aliasing would help.

Is that possible with Octane or is this a known issue?

Cheers

[bepeg4d]

Hi Teddi,
you can slightly increase the Filter value in the kernel settings, and set the Adaptive sampling Group pixels to 4x4 in PT.
ciao beppe

[Teddi]

Will try that thanks.