Noise in cryptomattes

[SonyBoy]

We've been testing out cryptomattes here for a while in the hope that we could use them to replace our explicit ObjID RGB mattes. While they mostly work well, in a couple of cases we've experienced some pretty nasty noise within certain areas of the cryptomatte passes. Is this just a sampling issue, or is there another cause? Our samples are already set pretty high, and without noise in any of the other channels, including the corresponding RGB matte for the area or object with the problem. We are using Nuke with multichannel EXRs, although the noise is visible in the RGB of the cryptomatte pass in any player. We're using Maya 2018.2 and Vray 3.60.04 on Windows 7.

[tashko.zashev]

Hi,

It's difficult for me to say what might be casing this high noise level in the Cryptomatte element without the scene. Is see that your settings are pretty high now, but have you tried to increase the Min. subdivisions. You can try a quick region render with 4 or 5.
If nothing helps, please send us the scene to support@chaosgroup.com

[SonyBoy]

Thanks, I'll try this and if this doesn't fix the issue I'll get back to you. The strange thing though is if I recall correctly the noise would often appear right in the center of an object. I would think that increasing the min subdivisions might help around edges, but not in the center like this?

[SonyBoy]

Actually came across an example this morning, see attached. Those big red squares in the center of the cross shape are what I'm talking about. Did a few tests with settings and it seems to be anti aliasing related as changing the filter type will change the size of the squares (Gaussian and Cook Variable will reduce their size, but not eliminate them). Cranking samples up or threshold down has no effect.

[tashko.zashev]

Can you do a quick test with Embree off to see if those red and pink squares will disappear?
It would be very helpful for us to try your file here? Would it be possible to upload it here or send a link to support@chaosgroup.com ? I believe that we have a fix for this in the V-Ray Next versions.

[SonyBoy]

Turning off Embree does seem to fix it -- thanks! I can't send you the entire file so attempted to strip one down with just that errant piece of geo in it. However, when I did that the problem went away, with or without Embree turned on. Strange -- does that tell you anything?

[tashko.zashev]

OK, this should be fixed in V-Ray next builds according to our developers and you can use the workaround for 3.6. But to be 100% sure about that and we are not missing something we can test the original scene here if you decide to send it over.