Cryptomatte virgin here. Anyone got a quick start pls?
this is the video I used. the big thing is you HAVE to use the color picker that is used in the video, and you need autokey off or to make sure you don’t create extra keyframes.
that said, I believe the node is now native in Flame, so it might be simpler now.
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Here’s @La_Flame’s excellent Flame Learning Channel video on the native Flame node:
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Does the cryptomatte render have to be 32bit?
Not necessarily.
It works at 16-bit
Perfect, thank you. My archives has been crazy large and that will help massively 
I believe I have just proven myself wrong.
I am looking into DWAA compression and during my investigations i was getting multi-layered EXRs containing cryptomattes.
I must have been mistaken back in Jun’21 because even though my EXR appears to be 16-bit the cryptomatte is actually 32-bit. CG informs me that it isn’t possible to make a 16-bit cryptomatte.
Always happy to learn and never ashamed to admit I made a mistake 
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I have another update for you.
I’ve been getting a real mixture of cryptomattes recently. Some with too many layers and some with too few so I thought that I would share my findings.
The cryptomatte needs to be supplied to Flame with only 7 inputs. 1 preview layer and 6 more inputs
Too many will work most of the time but with a loss in data and certain areas will be missing and unable to be selected.
Too few just won’t work for you.
The problem seems to be that different renders deal with them in a different way.
You should ask for the preview layer to be turned on. This has nothing to do with the maths of the selection but it does help you when selecting but isn’t essential to having it work.
When preview is off you can pipe in the beauty and use this to help you select areas.
Cryptomattes in Redshift
Ensure that the preview layer is enabled and set the cryptomatte level to 3
This will give you the preview plus 3 RGBA levels making 7 in total.
Cryptomattes in Arnold
Ensure that the preview layer is enabled and set the cryptomatte level to 6
These 6 plus the preview makes 7 in total.
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Thanks for the info Richard! That will help. Have you ever had jaggy edges with Cryptomatte? That’s what I’m fighting right now.
Jaggy edges 
No not had that problem.