Problem with Background layer and overbright pixels with either denoiser or Lens Effects

[dlparisi]

I'm encountering a problem when I have a background layer enabled and have overly bright pixels. The bright pixels come from lights that are really bright, like 50000-250000 lumens bright. It's most noticeable when I have lens effects enabled but the issue is still evident at the edges of overbright pixels whenever the denoiser is on as well (see second image around the edges of the sphere light).

Lens Effect and Intel Denoiser:

Intel Denoiser Only:

Lens Effect and Nvidia Denoiser:


Oddly, I don't get any lens effect at all when I have the V-Ray Denoiser enabled with a background layer but at least I don't get any off color pixels. It also seems weird that I get a different lens effect between the Nvidia and Intel denoiser, almost like the math is off or it's clamping it somewhere. Any ideas?

Soooo, what could be causing this and is there some workaround? I usually just composite the render over the background in photoshop but for the scene I've got going right now photoshop "compositing" wasn't cutting it so I decided to do it mostly in the VFB. FYI, this is not the actual scene I'm working on, just a test.

Basic scene attached. Replace the background with anything since it didn't seem to make a difference for me.
Overbright Pixels test.zip

[dlparisi]

Small update... I can get everything to work as expected with no aberrant pixels if I set up the VFB as a composite with a Back to Beauty Pass and add the background to the Composite rather than the standard layer list. Seems like a bug perhaps for the method noted above.


Minor clarification: I need to put the Background layer at least below the Self-illumination layer in the composite stack in order for everything to work correctly otherwise the two lens effects don't match (nvidia and intel denoiser) and don't show at all with the vray denoiser.

[hermit.crab]

Thanks for the report. It seems that using the NVidia/Intel denoisers and a Background layer on top of it yields a bad result. The default V-Ray denoiser engine seems to be correct - the background on top should obscure the lens effects. I've logged the issue (internal bug-tracker id: VMAX-13831) for developer investigation. The Composite method can be used as a workaround.

[dlparisi]

Just to clarify, I think the lens effect on the Nvidia denoiser version looks correct when compared to versions without the background enabled. It's the Intel one that looks incorrect IMO and I don't get any lens effects when using the Vray Denoiser.

What about the odd pixel values that are evident in both versions where the lens flare meets up with the light source?

[hermit.crab]

Just to clarify, I think the lens effect on the Nvidia denoiser version looks correct when compared to versions without the background enabled. It's the Intel one that looks incorrect IMO and I don't get any lens effects when using the Vray Denoiser.

In my tests, both NVidia and Intel exhibit the issue. With the default V-Ray denoiser, the Background layer is obscuring the Lens effects, hence why they seem invisible - it should be like that for all three denoisers. This explains why the Composite method works for all three - the background layer is below the lens effects.

What about the odd pixel values that are evident in both versions where the lens flare meets up with the light source?

If you zoom closely at the edges of the light, there seems to be some anti-aliasing occurring with Nvidia/Intel denoisers, which ends up in the odd pixels in the result. Probably a secondary effect from the core issue.

[Alex_M]

Not sure if it's related to the same problem or not, but I'm also getting weird artifacts over my rendered objects whenever I use the "Background" VFB layer in combination with the Intel or Nvidia denoiser. Please check the screenshots below. If I use the Vray denoiser or no denoiser at all, I don't get these artifacts.

[dlparisi]

Yeah, not sure if it's related to the lens effect problem I am having either.

For your issue though, what does your alpha look like? Any weird holes in the problem areas? I've noticed that the Nvidia denoiser sometimes introduced noise into solid parts which lets the background bleed through, which may or may not be your problem.

[dlparisi]

Double post...

[hermit.crab]

Not sure if it's related to the same problem or not, but I'm also getting weird artifacts over my rendered objects whenever I use the "Background" VFB layer in combination with the Intel or Nvidia denoiser. Please check the screenshots below. If I use the Vray denoiser or no denoiser at all, I don't get these artifacts.

Seems very similar. I'll add your report to the tracker as well.

[Alex_M]

Yeah, not sure if it's related to the lens effect problem I am having either.

For your issue though, what does your alpha look like? Any weird holes in the problem areas? I've noticed that the Nvidia denoiser sometimes introduced noise into solid parts which lets the background bleed through, which may or may not be your problem.

Yes, I've seen artifacts sometimes appear around the edges of the alpha channel. It happens when I use the Intel denoiser (I very rarely use the Nvidia denoiser). Interestingly, this started happening recently. I think it was when I installed V-Ray 6 Update 2. I'll send a scene and some screenshots when it happens again.