AndrewHazelden
commented
6 years ago Hi Fredrik.
I would now like to render this out from Nuke into another EXR file and still maintaining the (otherwise untouched) Cryptomatte channels. It seems this is possible only if I set the "datatype" to "32-bit" float and also setting "metadata" to "all metadata" in the Write node. If I instead choose "16-bit half", the re-written EXR cannot be used with the Cryptomatte Nuke plugin.
With V-ray 3.6 based Cryptomatte renderings coming out of your 3D package, it is possible to have an EXR image that stores mixed bit depths in the same file.
The RGB "beauty" channel can be set to either 16 bit Half-float or 32-bit float per channel image data.
V-Ray will automatically set the Cryptomatte matte channels in the EXR image to be rendered at full 32-bit float depth regardless of any options you set in your 3D package.
To the best of my knowledge, Cryptomatte always needs its matte channels to be stored as full floating point 32-bit channel image data to function correctly. This means you should never intentionally degrade the bit depth of those "cryptomatte##.R,G,B" image channels from 32-bit down to 16-bit during your Cryptomatte centric compositing tasks in your compositing package.
For the benefit of anyone else reading this GitHub issues post, here is a sample V-ray for Maya Cryptomatte EXR rendered image I created that shows this concept of the mixed bit depths in the same file:
If you open up this V-ray rendered EXR image in a tool like DJV_View and browse through the image channels you will notice this mixed bit depth thing happening.
This is a screenshot of the "crypto_vray_balls_test.exr" image loaded in DJV View with the RGB channels visible. On the bottom right of the window is the text "RGBA F16" which means you are viewing a half-float 16 bit per channel image.
If you go to DJV Viewer's File > Layer menu and select the "Cryptomatte.R,G,B,A" channel in the image you will see the text on the bottom right of the window is showing "RGBA F32" which means you are viewing the Cryptomatte based matte channels as full 32 bit per channel floating point images:
I'm not a Nuke user so I can't comment on best practices but I'd have to guess that you'd likely need to render out to a full 32-bit per channel output for all image channels in the Nuke Write node if you want your RGB beauty pass images to be stored at the same bit depth as the Cryptomatte 32-bit float channels are natively.
The Cryptomatte for Nuke developers can chime in here and clarify that point.
Regards, Andrew Hazelden
fredrikaverpil
jonahfriedman
tokejepsen
I'm rendering multichannel EXRs from V-Ray and I can successfully pick my objects using the Cryptomatte Nuke plugin (v1.1.4).
I would now like to render this out from Nuke into another EXR file, still maintaining the (otherwise untouched) Cryptomatte channels. It seems this is possible only if I set the "datatype" to "32-bit" float and also setting "metadata" to "all metadata" in the Write node. If I instead choose "16-bit half", the re-written EXR cannot be used with the Cryptomatte Nuke plugin.
Questions
EDIT: So, yes, using e.g. Nuke 10.5v6 I can render out 32-bit float EXR files and still maintain the Cryptomatte channels perfectly fine. You also need to set metadata to "all metadata" in the Write node. Nuke can not write out a "mixed bit-depth" EXR, unfortunately, so even if many channels are 16-bit half, I'll have to write out a fully 32-bit float EXR from Nuke.