Denoised image becomes worse after doing region renderings

[Alex_M]

I've noticed that when I use Nvidia Denoiser and do region renderings, the image outside of the region becomes all weird with halos and blocky artifacts, especially around edges. This have happened a few times now on different scenes. Please check the screenshots below.

[hermit.crab]

This is the normal Nvidia denoiser behavior - it generates the denoising elements for the region, however, its effect is estimated for the image outside the region (due to the lack of denoising information). A similar thing happens with the V-Ray denoiser, where the pixels outside the region are erased (not as trivial to improve, I'm afraid). When saving the image the original RGB is kept (Note that saving through the V-Ray raw image file option saves only the selected region. To resolve this add a VRayOptionsRE, where the EXR data window mode is set to Whole Image) and it may be used for the composition with the denoised region for the desired effect. Do tell us what is the reason for using this kind of workflow, rather than denoising the whole image?

[Alex_M]

I think I found what causes this! Please check the screenshots below. The diffuseFilter channel shows the information that should be in the bumpNormals channel and the bumpNormals show the Glare channel but with grey color cast. You can clearly see that only the region has the correct information for the respective channel. No wonder the denoiser bugs out on the image that's outside the region. To me this looks like a bug, or? Moreover, it happens only from time to time. For example, I've just did a few tests and I couldn't get Vray to mix the channels' information like that again. Let me know if you need the VRIMG file or the whole scene.

[yavor.rubenov]

Hello,

I think I found a way to reproduce this:
- Render and save some image to history with some render elements
- Later on - load the saved image from history
- Change the render elements in the scene - f.e add new elements or remove some of them. In my test I had 2 MutliMattes and the NVidia denoiser in the history image. In the scene I removed one MultiMatte element.
- Render some region

In that case - the data inside the region is correct for all channels but outside the region channels are mismatched.

Does this sound like something that might have happened in your case ?

We'll try to fix the described problem soon and get a fixed build ready.

Best regards,
Yavor

[Alex_M]

Yes, that's exactly the behavior I'm seeing across many different scenes! Thanks for troubleshooting this, Yavor.

[yavor.rubenov]

Sorry for the inconvenience - will try to get a fix ASAP.

[Pixelcon]

I know it's only been a month since this was brought up but this issue is borderline crippling. Region rendering is more or less unusable as it stands...

[yavor.rubenov]

Sorry I didn't write in this thread - you can try the stable nightlies - they should contain the fix.

[Pixelcon]

Sorry I didn't write in this thread - you can try the stable nightlies - they should contain the fix.

Excellent! Thanks Yavor