Cryptomatte Single-Channel EXR Usage in Nuke

[selavfx]

Hi,
since single-channel EXR files with DWA compression are now supporting Cryptomattes in Vray 3.60.04, we would love to use them in production instead of using multichannel EXR files.
Usually with a multi-channel file, we were able to simply shuffle out the cryptomatte AOV from the readNode in Nuke, hook up the latest Cryptomatte-Gizmo and pick the color to extract the matte.. so far so good.

Now with single-channel EXRs files, we are reading the first of the cryptomatte AOVs, connecting it straight to the Cryptomatte-Gizmo and trying to pick the colors .. unfortunately without success. Nothing gets added to the matteList - it looks like there is no manifest written within that AOV.

Am I missing something fundamental?
Can someone please enlighten me, how to use the single-channel EXR cryptomatte AOV in conjunction with the Cryptomatte-Gizmo in Nuke !?

This is Vray 3.60.04, Cryptomatte for Nuke 1.2.0, OpenEXR with DWAA compression.

Thank you!

[vlado]

I believe the Cryptomatte gizmo in Nuke only works with multi-channel OpenEXR files. You need all the Cryptomatte elements (not just the first one), as well as the additional manifest attributes written to the OpenEXR file. You can probably ask on the Cryptomatte Github - the Cryptomatte authors can probably tell you more.

I'm afraid moving to a multichannel pipeline is inevitable in the long run. I know that some users want to stubbornly ignore this fact, but I think it's just a matter of time

Best regards,
Vlado

[selavfx]

Thanks for the quick answer and explanation Vlado, I'll probably check with the cryptomatte guys if they could provide sth..

I'm actually fine with rendering multi-channel files, but I was always under the impression that they have a big impact on performance in Nuke - at least most of the Compers I know weren't happy with having multi-channel files in comparison to single-channel EXRs, but that might have changed with more recent versions of Nuke/EXR !?

I guess I have to do a little performance comparison test and try to convince some people

Cheers!

[vlado]

For maximum performance with multi-channel OpenEXR files, add a VRayOptionRE render element and turn on the "exr multipart" option. This will export the files in a format that is faster to read in Nuke (but will make them incompatible with older software that still uses version 1 of the OpenEXR library).

Best regards,
Vlado

[jasonhuang1115]

For maximum performance with multi-channel OpenEXR files, add a VRayOptionRE render element and turn on the "exr multipart" option. This will export the files in a format that is faster to read in Nuke (but will make them incompatible with older software that still uses version 1 of the OpenEXR library).

Best regards,
Vlado

vlado I am running Vray 3.60.04 on Maya 2018.2 and couldn't find this VRayOptionRE render element from the Available render elements list in Render Settings window>Render Elements tab. Is this in Maya or Max or only available in the Next?

[vlado]

vlado I am running Vray 3.60.04 on Maya 2018.2 and couldn't find this VRayOptionRE render element from the Available render elements list in Render Settings window>Render Elements tab. Is this in Maya or Max or only available in the Next?

In Maya, the multipart option is available in the "Image format options" dialog (see attachment).

Best regards,
Vlado

[selavfx]

Thanks Vlado, thats great info!
I'll definitely check that out.

[jasonhuang1115]

vlado awesome! Thanks for the pointer and screenshots.