High noise level

[nikoni]

Hi all! Finished this render now but for some reason at 2.5% noise lvl and 1.0 denoise factor the picture is terribly noisy, but such elements like a bedside table are absolutely clear. I'm wondering what could be the problem, this is not the first time i encounter it. Illuminated with corona sun and standard sky environment. The render was made in Corona 10.

[maru]

Such lighting scenario where the only light in the scene is entering through a small opening and then is scattered by a semi-transparent/translucent material is extremely hard to sample. Make sure that you are using UHD Cache as the secondary solver in the Performance tab, and if you need to have exactly this kind of lighting setup, the best solution would be using the Rayswitch Material to make the translucent curtain appear as it is when seen directly, but simplify it for the GI rays. For example, depending on your current setup, you could use transparency instead of translucency.
Here is more information:
https://docs.chaos.com/display/CRMAX/Corona+Rayswitch+Material
https://docs.chaos.com/display/CRMAX/Corona+Rayswitch+Map

If you are fine with getting better render times but changing the appearance of the scene a bit, you could also place an additional light inside the room, close to the curtain. It should make the overall lighting more uniform and easier to sample. You could also add some additional light sources in the room as "fill in" lights.

[nikoni]

Oh i see! But why does some objects have no noise, while others do?

[romullus]

Hi all! Finished this render now but for some reason at 2.5% noise lvl and 1.0 denoise factor the picture is terribly noisy

If you're using Corona HQ denoiser, then check if image filter is set to High Quality. I had similar renders where Corona denoiser did terrible job when image filter was set anything but High Quality. On the other hand i would recommend to try Intel Open denoiser, at the moment it does better job than Corona HQ.

[maru]

Oh i see! But why does some objects have no noise, while others do?

The Corona HQ denoiser is less aggressive on materials which are using bump maps. The ones without bump maps will get "smoother" denoising.

[nikoni]

Okey, i see! Thank you very much for help!