frozen pattern within fire

[finalight]

I'm getting a frozen noise pattern down inside the fire of an explosion sim. I haven't seen this before version 4.0 and am trying to isolate it. I've tried many different combinations of render steps, jitter, Vray AA, etc. and am not able to remove it. This sim has a lot of detail, hence it's not due to step/voxel issues from a low resolution sim. I'm using version 4.0 on this box. I'm going to test further, however any ideas would be helpful. Here's a screenshot. Thanks!

[finalight]

Problem seems to resolve using Scanline renderer, or at least I'm not seeing it. Any known issues with Vray and FumeFX 4.0? Thanks!

[sitnisati]

Hello,

Scanline and VRay are using the same FumeFX functions, so not sure why VRay would render different.
Does all VRay AA engines produce the same effect ?

Regards,
Kresimir Tkalcec

[finalight]

HI Kresimir,

Yes, all Vray AA engines render it that way. Below is a render crop from a sim showing the difference between the VR and SL renders. Also, here is a cropped short render range comparing each - you'll see the locked pattern down inside the Vray version and barely perceptible if at all in the SL version: http://vfxfactory.com/images/frozenNoise...VRvsSL.zip. I realize the SL render below has deeper darks, however you'll see the problem readily in the render test as the fire is moving. Thanks again.

[sitnisati]

Hello,

I have checked the VRay's sequence and I must admit that I cannot spot any artifact/pattern there...
Could you maybe create some longer video that clip we can check ?

Thank you.

Regards,
Kresimir Tkalcec

[finalight]

Hi Kresimir,

If you play the Vray sequence back at about 15 fps you'll see a frozen organic noise pattern down in the fire that appears locked - it never changes. I'll try to get a longer sequence rendered out, however it looks just like this. Thanks.

[finalight]

I fell back to Fumefx 3.5.4 for rendering and the problem went away with Vray. I guess for now I'll sim in 4.0 and render in 3.5.4 since 4.0 has better simming features. I'm also noticing I have to change the fire shader a lot when Vray rendering Ffx 4.0 - color values are much higher - in comp I have to bring the unclamped float values way down. In 3.5.4 switching between Scanline and Vray yields identical color values. Seems to be something going on with Vray and Fumefx 4.0 when rendering.

[finalight]

Any word on this? Are there any known issues with Vray and Ffx 4.0? Thank you.

[sitnisati]

Hello Brian,

Please find attached example image with FumeFX 4.
Both Scanline and VRay seems to render the same.

Regards,
Kresimir Tkalcec

[finalight]

Hi Kresimir,

It must be this node. Very strange.

Thanks much.

[sitnisati]

Not sure what might be the cause for this as Scanline, finalRender and VRay use the same FumeFX' shading code.
Maybe it's something with gamma correction ?

Regards,
Kresimir Tkalcec

[finalight]

Yep, I was hitting my head against the wall trying to figure this out. Was checking gamma and Vray params. Jury is still out on this one. I do need to update Vray so perhaps it's something with the older version on this node.