New Octane version has black border around transparency

[Hurricane046]

I don't want to put this to bug report because it might just be issue on my side but is there any reason for the black border being present in the render on the latest Octane version? This problem is not present on older one where everything works as it supposed to.

Here are examples from the same scene, same Octane render settings, everything is the same except the resulting .exr output is different - the difference being the transparent objects suddenly have black outline.

I have attached simplified .c4d files for testing (see bottom of the post for download). This zip includes the output .exr files also.

Thank you for any kind of help. I've been at this for 4 hours and for the life of me I cannot get rid of the outline in the .exr files.



EDIT 1: Done more lightweight testing. I still cannot get rid of the black border in the new version. It's even more prominent when you use white material.



EDIT 2: Yeah I'm pretty certain new Octane can't output proper alpha OR some internal feature was changed and now we need check some boxes perhaps to get rid of this? I've used pretty much the same render settings and Octane setup on hundreds of CG shots across the years and never once had this issue before.

[skientia]

I don't want to put this to bug report because it might just be issue on my side but is there any reason for the black border being present in the render on the latest Octane version? This problem is not present on older one where everything works as it supposed to.

It could be a user-error or a post-software issue of some sort (bug, misinterpretation of transparency or improper support).

Nothing in the 2024.1 release notes mentions a change related to "alpha" encoding. This page's demonstrations were made with Octane Standalone 2024 (stable). This would rule out Octane "core", but does not exclude a plugin-specific issue. The page contains information on the proper way to handle "Alpha" out of the renderer and in post, and can be used to double-check everything.

It's even more prominent when you use white material.

This is likely a case of perceptual difference, more noticeable due to the higher contrast ratio (white material perceptually makes the darker outline emphasized).

Perhaps, an AE-related issue.
Testing in another more or less VFX compliant software would rule it out (Fusion, Nuke or for free, the Blender compositor).

As the EXR export encoding specifications were not provided: as long as the "alpha" is encoded as associated "premultiplied alpha" , it should be correct provided that the software for post is properly supporting "transparency" and is correctly setup.

[Hurricane046]

I'll throw this at our TD tomorrow so he can run this through Nuke and we'll see if he can figure it out. For now we're running renders on the older version just to be safe.

I've never felt need to alter my render settings preset since like 95% of my works were rendered on these same render settings across the years and were comped on the same AE setup but I came to work today and found that all my overnight renders containing transparency contained this strange black outline after the update.

[aoktar]

"Disable partial alpha" in imager may solve your issue!

[jayroth2020]

Render Settings > Octane Renderer > Main > Premultiplied Alpha — change to None.

[Hurricane046]

Our TD had a look at the issue. He wasn't able to get the alpha working either. His preliminary results on simple fresh scene with cube on transparent background:



EDIT: He's now sure the new Octane is unable to export straight alpha. The beauty pass is already premultiplied and he can't get straight beauty pass .exr out no matter what.

If anyone could share simple .c4d test scene with a blurry cube where alpha exr works properly (on new Octane version) we'd love to test this issue further!

[Hurricane046]

REPLICATED

We've narrowed this problem down the Denoised beauty checkbox. It definitely breaks denoised alpha exr output in the newer Octane version WHEN USING OCTANE AI DENOISER. The alpha works correctly WHEN USING OPEN IMAGE DENOISER.
I'm pretty sure it has something to do with the updates that have been discussed here. - Powerful denoise AOV nodes and filter graphs (GPU and CPU)

EDIT: We consider this issue solved and switching all our scenes to Open Image Denoiser. I'll do another batch of overnight renders with the Open Image Denoiser and post update tomorrow!

[skientia]

"Alpha" is not "supposed to be straight" but associated, a.k.a. (the widely adopted misnomer) "premultiplied".

About Denoising Issue (2024.1.1)
This post is seemingly facing the same issue. Quote:

OctaneRender 2024.1.2 has been released: viewtopic.php?f=24&t=84359

Changes since 2024.1.1

Fixes

• Fixed denoised render AOVs and volume mask render AOV containing an unintended alpha premultiplication when kernel alpha channel is enabled.

[Hurricane046]

Thank you for the response skientia! We'll finish current projects on the 2024.1-[R3] version then and update to the fixed 2024.1.1.

EDIT: SOLVED
Fixed and tested in Octane 2024.1.1 and up. Happy rendering!

[frankmci]

Man, I love reading a thread like this. So satisfying. Nice work, everybody!