the trouble with volumetrics

[sirogi77]

Hey all

Have a simple volumetric setup:
envFog with density mapped to some 3D noise
lit by a couple of lights, through a rotating fan to get some moving beams of light.
trouble is, I also get some weird sparkly artefacts. (check out the image.)
tried everything I could think of, any help is appreciated.

[bazuka]

so far as i could check here, probl is simple, just hide ur rect light and u wont have a probl with noise...

i think ur light has too low sampling...

p.s. i just set the sampling to 32 and everything looks fine here

cheers

[sirogi77]

thanks for taking a look.

Unfortunately I had already tried to hide / show the spot light and the rect light, various pieces of geometry, nothing does it.
it's not the noise per se that's the problem, more like the black artefacts.
Tried cranking up the subdivs on the light, completely removed the spotlight with soft shadows, played with the threshold and the max subdivs in the render globals....
nothing does it. I always get those pitch black pixels.

almost like an internal math error that's not related to anything.. your render -is- artefact-free though

any ideas?

[sirogi77]

Taking the fade out radius on the envFog back down to 0 fixed it.
still.. weird.

[bazuka]

i have even low down the fog sampling, i could send u scene if u want...

[svetlozar.draganov]

http://dl.dropbox.com/u/45398240/Cha...on_fan_v004.mb

It seems this noise is mostly from the Vray Image Sampler.
The parameters which control the amount of Atmospheric noise in your scene are :
1)Threshold in Adaptive DMC Image sampler + Min and Max subdivs
2) StepSize in Raymarching Roll-out in VrayEnvironment Fog Parameters

Of course decreasing the amount of noise increase rendering time. You can use the above parameters to adjust the amount of noise vs render-time!