Denoise issue with multi-layer EXR

[simon_lundberg]

I have a render pipeline that depends on rendering to multi-layered OpenEXR files instead of multiple single-layer files. The only way I've been able to do that in 3ds Max is by using the "raw image" output and setting that to OpenEXR. That mostly works, but the main RGBA output is *not* denoised, and only the main RGBA layer actually has an alpha. All the other layers are just RGB. So if I render to "raw image", by denoised alpha seems to be just... gone? I have of course turned on "denoise alpha" in the denoise settings, and if I render to just a single layer or to multiple files the alpha is indeed denoised. It's just when rendering to "raw image" that it's gone.

Is there some other way to render to multi-layered EXR? I kind of need to get this working asap.

[Vizioen]

I don't use denoiser, so not sure if what I'm saying might help, but what happens if you enable 'Create Effectsresult' channel in the Lens Effect layer in VFB. Does that provide you with a denoised alpha on that layer?

[Joelaff]

If you set the denoiser to only generate render elements and then render as you are with the “raw” output saved to EXR then you can use the standalone denoiser to denoise afterwards. This works well for us.

[simon_lundberg]

I don't use denoiser, so not sure if what I'm saying might help, but what happens if you enable 'Create Effectsresult' channel in the Lens Effect layer in VFB. Does that provide you with a denoised alpha on that layer?

The effectResult layer is created automatically as long as you have a denoiser, but it lacks an alpha channel.

If you set the denoiser to only generate render elements and then render as you are with the “raw” output saved to EXR then you can use the standalone denoiser to denoise afterwards. This works well for us.

That's actually a good idea! It also means I could speed up the denoising a lot because the stand-alone OIDN denoiser supports GPU devices. I'll look into that. Unfortunately it's also a pretty big pipeline change. Still, that might work. Thanks!

[Joelaff]

Oh, are you using the standalone denoiser direct from OIDN? I have not tried that. We have been using VRay’s vDenoise to denoiser with the Open Image Denoiser (run it from the command line to see the arguments, as the documentation is not up to date online, and it does work with multiple elements).

Maybe I should look at the one from OIDN if it is using the latest version, because vdenoise is not on the latest version, and will not use the GPU (though it is pretty fast compared to the VRay denoiser). But I assume the latest version may be better in other ways as well. Not sure if Chaos trained their version for VRay renders specifically or not.