Vray 5 applies denoiser twice, heavily blurring the image in the process

[Alex_M]

Yet another bug. I've just rendered an image and everything was great. Then I noticed something in the scene that I needed to change and so I had to do a region render. However, after the region render completed, Vray denoised the denoised result, heavily blurring the image in the process. I used Vray's denoiser. Please check the screenshots below.

Here's what I did:

1. I enabled resumable rendering and rendered the high-res image.
2. After the rendering finished, I saved it in the VFB history.
3. I saw some issues with the concrete backsplash and after a bit of adjustments with IPR, I decided the image was now ok, so I cleared the image in the VFB, and then loaded back the high-res image that I saved in VFB history eariler.
4. I then disabled resumable rendering, selected the concrete backsplash object, set Render Mask to "Selected", drew a region around the backsplash and I started the rendering.
5. After rendering finished, Vray applied denoising on top of the denoised result.

What's interesting is that the backsplash which I rendered with Render Mask Selected didn't get denoised twice.

[hermit.crab]

I'm getting odd results with the Nvidia denoiser, presumably because of the behavior explained here, however, this does not seem to happen with the V-Ray denoiser (also explained in the linked topic). Send the scene to support@chaogroup.com so we can take a look.

[Alex_M]

I've just sent you the scene. Ticket number is 316-060-7818.

[yavor.rubenov]

Hello,

Thanks for the scene - with it it was fairly easy to understand what is going on.
The already mentioned bug with channels mixup after loading images from history happened here too (doesn't matter that you didn't change render elements in the scene itself). As a result the defocusAmount channel (which is mostly white in that part of the scene) ended up in the noiseLevel channel. Then since you are rendering with Render mask selected only the backsplash object got rendered and all else was left with the wrong info. As a result the noiseLevel channel became something like this:
where the mostly black part is rendered and the white part is due to the mixup and contains defocusAmount data.

After that the denoiser uses the noiseLevel to determine denoising strength with white being full strength - this leads to the heavy blurring.

Sorry again for all the trouble this bug caused.

Best regards,
Yavor

[Alex_M]

Very good explanation, makes sense. Thanks. Hopefully the fix makes it in the upcoming update.