Noise that never cleans up

[Jpjapers]

Its probably a very technical question, but howcome in some instances (usually with emissive materials) you end up with noise that never disappears?
Was just curious :)

[Beanzvision]

Perhaps these might help? ;)
https://coronarenderer.freshdesk.com/support/solutions/articles/5000501983-how-to-get-rid-of-excessive-noise-
https://coronarenderer.freshdesk.com/support/solutions/articles/5000515603

[Jpjapers]

Perhaps these might help? ;)
https://coronarenderer.freshdesk.com/support/solutions/articles/5000501983-how-to-get-rid-of-excessive-noise-
https://coronarenderer.freshdesk.com/support/solutions/articles/5000515603

Thanks, I know when and why i am supposed to use the different materials i was just curious as to the actual reason why it doesnt clean up.

[lupaz]

I'm interested in this question too.
In another (GPU based) render engine, the more you wait for the rendering, the more it cleans up. With Corona that doesn't seem to be the case, no?

[Christa Noel]

No you're wrong. Every progressive render engine will cleans up noises following the time, and so does corona which uses progressive engine only. since bucket engine was removed long time ago.
About Jpjaper's case, it is too difficult to help with very limited information. Imho a simplified scene will be more than enough.

[lupaz]

Hi Christa.

Every progressive render engine will cleans up noises following the time,

If I'm not mistaken, every progressive render engine will clean up noise following the time with limits set in advance for the adaptive sampler.

In corona "By default, in Corona Renderer there is no limit set for its progressive rendering"
Is there a noise threshold?

[lupaz]

On this thread:

https://forum.corona-renderer.com/index.php?topic=10851.msg69498#msg69498

Someone asks for this:

-> setting level of noise / color threshold
  - pros: guaranteed image quality, even at multiple image render, no need to check the progress on production renders for quality
  - cons: well, time is anyone's guess again

Maru says:

...For a better solution we still need to wait for proper adaptivity.

And Ondra replies a few months later with "done".

I guess my question would be, why does corona stop working on certain areas even when there's still noise present, regardless the cause?
Shouldn't the adaptivity kick in only when the threshold is reached?

Is that threshold something we can reduce so corona keeps on working until the threshold is reached?

[maru]

Corona should still add samples to all pixels, even if they are "fine" according to adaptivity.
If there is a problem like persistent noise, please contact us with more details. Otherwise we cannot understand what we are dealing with.
An image showing the issue is the bare minimum. A scene with the issue reproducible would be perfect. (see my signature)

[lupaz]

Hi Maru.
Done. File uploaded.

Just click render. The selected region won't clean up after 400 passes or so.
I am aware that I have 4 panels of glass in front of it. Still it seems strange that the noise won't go away in less passes.

[Jpjapers]

I traced my issues back to a very small but very bright object with a light material on a filament of a downloaded lightbulb model that was reflecting on faceted chrome creating inordinate amounts of noise.

[lupaz]

I traced my issues back to a very small but very bright object with a light material on a filament of a downloaded lightbulb model that was reflecting on faceted chrome creating inordinate amounts of noise.

I had some of those cases too. Corona converts assets to coronalightmaterial directly. It could be nice if the converter suggests converting to self illumination or if light material with emit unchecked would behave like self illumination, and the converter asked if this is what you wanted.

[maru]

Hi Maru.
Done. File uploaded.

Just click render. The selected region won't clean up after 400 passes or so.
I am aware that I have 4 panels of glass in front of it. Still it seems strange that the noise won't go away in less passes.

So here is what I have found helps:

-set up the glass with rayswitch mtl like in my screenshot here
or
-lower reflection glossiness and refraction glossiness from 1,0 to 0,99

Both solutions are kind of strange, and it should not work like this.
I will forward the scene to the developers and we will see if we can optimize rendering in situations like this.

Thanks a lot for sharing the scene! I hope my workaround is useful for you and that you will get slightly lower render times thanks to it.

(internal note: id=240080028)

[lupaz]

Thank you Maru! I really appreciate your time.
If you guys have Corona 1.6 installed, could you make a quick try with it? I don't remember having this problem with 1.6 and would consider going back.
Thanks again.

[Jpjapers]

Interestingly enough i was also experiencing this issue behind glass