strange bright patches with preset clouds and bf/lc.

[anthonyh]

hi,
i`m getting some strange white areas/patches on a cloud preset sim using bf/lc. with im/lc they aren`t there. i`m not sure if this is a vray or phoenix thing so i thought i`d start here. i`m using a displacement too but the effect is more pronounced when off. on a side note brute force is rendering way quicker with phoenix than im/lc, not sure if that`s expected but it`s great.
thanks
anthonyh

[anthonyh]

i`ve just noticed, the more detailed the grid the more bright spots there are.
i rendered an animation and it`s extremely flickery, so light cache maybe ? i`ll bf/bf and see. ooh also getting odd squares where the render is different. this image is just rendered locally.

so volumetric rendering renders squares, switching it to volumetric geometry renders without squares.
hmm, even bf/bf animation is flickering badly ? now i`ve rendered with no gi and it still flickers. so i guess it must be phoenix ?

hi georgi,
i`ll send it over.

[georgi.zhekov]

Hello,

Can you get us a scene for this? You can attach it here or send it to support@chaosgroup.com

Thanks

[anthonyh]

sent to support email.
thanks Georgi
anthonyh
btw i am time remapping it pretty heavily. play speed 0.02. don`t know if that matters. they are clouds after all.

[flipbook]

I've found lowering the light cache speed up to about 0.1 eradicates the flickering. It was like an Irradiance Map flicker on the clouds.

[anthonyh]

hi flipbook,
great, thanks for the info.
it`s strange as i`m not actually using GI anymore, swapped for a dome light. i guess phoenix must precalc it`s own lightcache then because if you turn off use light cache in volumetric options it renders really slow even though in theory no lightcache is being calculated because GI is off ? anyway, at least i`ll hopefully be able to get it to render .
thanks
anthonyh

[georgi.zhekov]

Phoenix's Light Cache enables light caching for each voxel of the grid, which speeds up rendering considerably when the voxel size of the grid is significantly larger than the rendering pixel. If the grid resolution is large enough compared to the rendering resolution, disabling this option will speed up rendering.

Also, this feature might produce artifacts when the smoke is very dense, or when objects cast shadows through the smoke.

This option is unrelated to the V-Ray light cache and has nothing to do with GI.

[anthonyh]

hi georgi,
thanks for the explanation.
considering the clouds preset are quite dense and (on my scene) lowering the LC speedup to 0.1 isn`t removing the flickering on my end(i have resimulated at a different scale since sending that scene) it doesn`t seem like the cloud preset is set up for smooth animation at default ? what`s the best way to render without flicker ?
also what was with the render square inconsistencies when using just volumetric rendering ?
many thanks for looking at this.
anthonyh

[georgi.zhekov]

Hey,

For the flickering you can remove the Light-Cache speedup and it should fix it.

As for the light spots and the different buckets - I couldn't reproduce that. What version of V-Ray are you using? Are you using DR?

[anthonyh]

hi georgi,
ok i`ll try turning it off and rendering, the rendering time is way longer though. should this be off by default for animations or is my scene a particularly bad example ?
I`m using vray3.40.03 and phoenix 3.00.01. No DR. It renders the weird squares direct on load from the file i sent. It does it rendering locally and through backburner. it only does it on volumetric render. volumetric geometry works ok.
ok, i`ve found the culprit. i was using bercon noise plugin, the issue goes away with standard noise or using volumetric geometry.
thanks
anthonyh