Denoise vs beauty render grain

[seandunderdale]

Ive been finding my noise render settings arent equal when using a denoiser. If I render on cpu bucket mode with production settings, without denoiser, my beauty will look smooth. If I turn on denoiser, as its rendering, the same settings will look grainy. Is this normal? Once the render is finished and it denoises the render, its a sub standard version of the non denoised beauty (rather than a smoother version of the non denoised beauty beauty) I assumed the render should look identical as a base beauty, except the added denoiser reduces grain further on the render to which it is added.

Is denoiser assuming that since its switched on, it can make some noise approximations to speed up the beauty?

Im using Vray 5 hotfix 1 on Maya 2020.

[hermit.crab]

Is this happening with the V-Ray or NVidia denoiser?

[seandunderdale]

Ill need to check...I think its the Nvidia one. I had to stop using the Vray one since it blurred things through glass super aggressively, so my car driver and interior would turn into a blurry blob after the denoise ran, and the alpha through the windows went all blurry. This was using default amount of denoise also.

[hermit.crab]

Could you check if the difference in noise is present with the V-Ray denoiser (when comparing non-denoised vs pre-denoised images)?

[seandunderdale]

Vray mode doesnt seem to have the noise problem. It does have issues with destroying alpha channels through window glass if the radius is set to default. I always have to drop this way down in the custom value. Nvidia one tested again today for sure is way more grainy rendering the beauty.

[seandunderdale]

Here's a comparison between Nvidia and Vray denoiser alpha channels. To be fair, the Nvidia denoise at default settings is barely denoising at all, compared to the Vray one. Its making a grainy beauty, and hardly fixing the grain it caused. But the alpha channel is crisp, compared to the Vray one. Changing the radius amount in the framebuffer and recalculating the Vray denoise does not fix the alpha. This is usually how I would work...Id render with a default settings denoiser and tweak it in the framebuffer so I don't have to re-render to get the noise right, but it looks like it might not be working?

Re-rendering with a custom low radius goes a long way to fix the Vray Apha channel. Also, whats the reason behind the alpha channel in the Nvidia render having a tint?

[hermit.crab]

Regarding the Nvidia denoiser's pre-denoise vs non-denoise issue - I've logged it (internal bug-tracker id: VMAYA-10254) for developer investigation.
About the alpha's - could you attach the simplified scene here? Or send it via the contact form addressed to me in the subject with a link to this thread in the message.