Rendering Cryptomatte pass only Blender 2.8

Hi all!
I have a question, is it possible to render only the cryptomatte layers on a multilayer EXR? The only way I got it working was overriding with a black material over my whole scene.
I tried leaving the combined option unchecked, but still renders a beauty pass.
I there another way of doing this? Only asking because I wanted to render this fast

thanks for the help!

I have the same question… Any ideas? Thanks!

For something like depth we can always use a very low sample count, but since cryptomatte is sample depended I am not sure how this would work. Will try to find the time to experiment with this…

Never got an answer on this. So my approach was to just do what i said on my first comment. Also, i’m not sure cryptomatte is influenced that much by the samples. I mean i think i used 10 and worked just fine. I tried 1 and was unusable. Maybe give it a try with 10 and see if it works? Hope this helps!

Cryptomatte is not generated in a dedicated rendering step, it’s a byproduct of the normal rendering process. (and this is true of basically all passes in modern renderers). The low-sample render method is the correct way to do this. There’s no way to say for sure how many is enough, if your sample count was determined by something that needs camera samples like DOF/motion-blur, you may not be able to reduce samples at all. Some scenes might be fine with 10-20 samples though, every scene will be different.

You can also reduce light bounces since you don’t need to calculate that if all you care about is updating mattes. This can help performance a bit.

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interesting, I didn’t know how all of this works. thanks for your detailed answer J!