I’m facing a strange Cryptomatte issue in Blender and would appreciate any help.
Problem:
Scene renders correctly at 1920×1080.
Cryptomatte works perfectly in the compositor.
When I change the render resolution to 3840×2160 (4K) using the same source file, same render settings, and same output settings, the Cryptomatte pass stops working correctly after saving the render as a MultiLayer EXR.
What I’ve Checked:
Same .blend file.
Same View Layer Cryptomatte settings.
Same File Output settings.
Tried renaming outputs (e.g., OBJ00).
Verified render passes are enabled.
Issue only appears when rendering at 4K resolution.
Additional Information:
Cryptomatte works normally before saving at 1080p.
The problem seems to occur when reading the saved MultiLayer EXR generated at 4K.
I’m trying to use Cryptomatte for compositing and animation workflows, so reliable EXR output is important.
Question:
Has anyone experienced Cryptomatte metadata or MultiLayer EXR issues specifically at 3840×2160 resolution? Is there any known limitation, metadata problem, memory issue, or EXR setting that could cause Cryptomatte IDs to fail only at higher resolutions?
That sounds really weird, TBH I didn’t tested 4k + cryptomattes, but given how they work since mask are encoded per pixel in theory it shouldn’t change at all.
So either the problem comes from your file, or indeed blender is messing up something.
What would be super helpful is a test file so we can investigate. Try to either make a simplified version of your actual file or build one from scratch. This should already be informative.
If the problem still occur then this test file is probably going to become part of a bug report.
Last thing to check is to test with a latest Alpha build of blender so you’re sure the problem isn’t already fixed …
My first though would be that what changes in case of switching HD to 4K is the amount of VRAM needed to render especially if you have lots of passes. I’ve had issues with denoising failing in various weird ways when running out of VRAM without actually crashing. Maybe that’s what is happening with Cryptomatte here? I would try rendering with tiles to reduce memory usage. Update GPU drivers just in case as well, because that’s the thing to do for any problem really . I’ve also had issues with Cryptomatte when using a different version of Blender for compositing and for rendering. You are using the same version here, right?
Then there is this thing when you somehow process Cryptomatte passes in compositing(I don’t know, maybe you need to crop the render or something) - they have 4 channels each, that’s apparently important.
There are also 2 types of Cryptomatte nodes - current and legacy one. Do both fail?
[!question] “Cryptomatte pass stops working correctly” - what does that mean? How exactly?
something else worth testing is to try cryptomatte within the compositor, so you’ll know if the problem occurs when saving the file or if it’s native.
from the top of my head, some exr format are destructive and that could be the cause of the problem. 16bit vs 32 bits : I’m not sure it doesn’t create issues as well !
Make sure you don’t use any compression first ! Then test different compression algorithm !
I don’t recall such a bug, basically cryptomatte works by creating a hash / code per object/material.
So any slight change in rgba values of each crypto layer is going to mess with that.
PIZ works well indeed, but others that are slightly destructive like DWAA are going to mess the data.
Just for the sake of testing removing compression remove one potential issue, but yes when the problem is figured out it’s better to activate compression again, but just avoid lossy ones…
. I’ve also had issues with Cryptomatte when using a different version of Blender for compositing and for rendering. You are using the same version here, right?