Cryptomatte and separated channels

[renato_kliegergennari]

Hello everyone

I am switching to vray from Redshift for an animation project and I am struggling a little bit with the render elements + cryptomatte.
When I choose cryptomatte on the render elements it render 4 different channels for me instead of one.

As I could notice, when you render an EXR with multiple layers the cryptomatte works in Fusion for instance, but if you want to split the channels into different EXR files, it does not.
Am I doing something wrong? How is the right approach to it?


Using multilayered EXR files can slow the comp work a lot due the file size...

Thanks for letting me know!

[^Lele^]

As I could notice, when you render an EXR with multiple layers the cryptomatte works in Fusion for instance, but if you want to split the channels into different EXR files, it does not.
Am I doing something wrong? How is the right approach to it?

You should leave it as multi-channel, it's the way cryptomatte expects the file to be.

Using multilayered EXR files can slow the comp work a lot due the file size...

Not if they aren't tiled, no: in the case of scanline-saved EXRs, performance is identical to that of multiple files, as only the required data is ever loaded (in Nuke or Fusion, at least.).
When you save with either the raw file saver with the memory VFB active, or directly from the VFB (i.e. with a memory frame buffer containing the whole image), then images, including "thick" EXRs, are saved as scanline.

[renato_kliegergennari]

Thanks for the reply.
It means that if I have Memory frame buffer selected and save the EXR as a raw vray file, it should be fine to work with multi-layered EXR files?

[^Lele^]

Correct.
Should "memory frame buffer" be deactivated, then you'd not see the rendering progress, and if rendering in buckets you'd be saving tiled multichannel EXRs, which used to be very very slow and memory hungry, but got better a few years ago (with EXR v2), although still not as quick as scanline ones.