Render passes and noise question Tweet

[Banti]

I was wondering how noise "adds up" from the different light passes into the main pass.

Lets imagine the following: A simple interior scene, a living room if you will, with only 1 window.
There are 2 light sources. One is an HDRI environment-light coming in from the outside through the window.
The other is a big light plane under the ceiling.

Lets assume the HDRI light pass is really noisy (because the window is really small).
But the light pass from the light-plane is perfectly clean and noise free. Now, my understanding is that the main pass simply adds all the passes together. Does this mean the noise from all passes are also added? What I mean is will the noise from the HDRI be visible in the main pass even though the other light cleans the scene perfectly in its light pass?

[whersmy]

If I recall that`s correct. Though I usually have the opposite.. .ies spotlights clean up less faster than a HDRI.
Though the Denoised beauty pass usually cleans up the HDRI noise quicker than .ies emitters

[Banti]

If I recall that`s correct. Though I usually have the opposite.. .ies spotlights clean up less faster than a HDRI.
Though the Denoised beauty pass usually cleans up the HDRI noise quicker than .ies emitters

Thanks for the reply.

If I have an open scene than the HDRI is way faster than a single light plane and that makes sense because light is coming from everywhere. But in interior scenes with a samll window the HDRI takes really long and is quite noisy, which also makes sense because its very little light that comes into the room.

Also I dont really use IES lights, just simple big light planes, mainly under the ceiling, which cleans up the room really fast.

I was just wondering because sometimes it seemes the noise from the HDRI is not visible anymore in the main pass, and other times I can still see it....