Cryptomattes with non multichannel EXRs?

[SonyBoy]

I guess I already know the answer, but is there any way to render a functioning cryptomatte to a file format other than a multichannel EXR?

Normally this would be my workflow, but I am currently working in 4K and just find multi EXR file sizes too unwieldy at that resolution. However, I still want cryptomattes. Seems like multichannel EXRs are the only file format that supports them, is that correct?

I can think of workarounds such as rendering multis then shuffling everything out for comping, but it's all inconvenient. Is there any other solution? And more importantly, is there a reason that cryptomattes cannot be output as separate, useable files like any other pass?

[Morbid Angel]

Well in our case we render twice, once for beauty which only contains primary bty aovs, then second render is util which contains all the util aovs. You could argue that just rendering multiexr with just cryptomatte will do the job while keeping the exr size manageable. I think the way its implemented it required the meta data only exr can store. Additionally and while not ideal, but working with 4k on your local machine's nvme vs over network can greatly improve performance, up to a factor of x100. So often I would copy the offending 1TB of renders to my local nvme drive and comp with it, then repath to network for network rendering if needed.

[SonyBoy]

Yes, multiple renders to reduce monolithic file sizes obviously is another way to go if render resources make that feasible (which isn't the case for me). What I don't understand about the multichannel EXR limitation is that if you render into the VFB you get what appears to be a normal crypto pass no matter what file format you have set, but only multis store it in a way that is functioning. As you say, presumably there is metadata that cannot be encoded in any other file format.

As it it, I've since realized with this particular project I can probably revert to good old multimattes and IDs for my needs....

[hermit.crab]

is there a reason that cryptomattes cannot be output as separate, useable files like any other pass?

With the implementation of the new "Save Cryptomattes separately" option in the V-Ray Raw Image Output, you can save the Cryptomattes in a multi-channeled .exr of their own and delete the regular one (whilst saving parallelly through the Separate render channels, of course). Maybe it's a good idea to have an option to save ONLY the Cryptomattes. I'll talk to the product manager about this.

Yes, multiple renders to reduce monolithic file sizes obviously is another way to go if render resources make that feasible (which isn't the case for me)

Mutli-channeled .exr file size can be reduced by using DWAA/DWAB EXR compression from the VRayOptionsRE.

[SonyBoy]

I'm not familiar with that feature... will check it out, thanks. Where would I find that option? I'm on Maya 2023 and Vray 6.20.02.

So far as compression -- yes, good point. I often simply forget about EXR compression types. Perhaps switching the default from ZIP to one of those you mention would be a good idea too.

[hermit.crab]

I'm not familiar with that feature... will check it out, thanks. Where would I find that option? I'm on Maya 2023 and Vray 6.20.02.

Pardon me, forgot we're in the Maya forums. The option has not yet been implemented in Maya, but it will be in V-Ray 7.