Noise level limit can be used to stop Corona's progressive rendering once the specified noise level is reached. The noise level limit is available only if adaptivity is enabled (adaptivity is enabled by default and should never be disabled).
Setting a higher noise level limit will stop rendering faster and with more noise visible. Setting lower values will stop rendering after a long time and with less noise visible. Usually, values of 2-3 are acceptable for final renders. Higher values can be used for faster previews.
Noise level is detected every X passes, where X is the "Adaptivity recalculation" setting available in Development / Experimental Stuff rollout (3ds Max | C4D). The default interval of adaptivity recalculation (5) should work well and there is no need to change it.
The noise level limit and noise level in Corona VFB are expressed in percent.
To learn about other progressive rendering limits see:
How to set limit for rendering? ( 3ds Max | C4D )
Examples
1. Noise level 100.
The rendering was stopped after 5 passes (adaptivity recalculation interval - this is the default setting) when the noise limit of 13% was measured.
Time: 01:29
2. Noise level 10.
The rendering was stopped after 10 passes when the noise limit of 8,9% was measured.
Setting the noise level above 13% would not make sense as the rendering would be then stopped at the same noise level as in the previous example (13%).
Time: 02:31
3. Noise level 5.
The rendering was stopped after 35 passes when the noise limit of 4,9% was measured.
Time: 07:39
3. Noise level 3.
The rendering was stopped after 95 passes when the noise limit of 3% was measured.
Time: 18:45
4. Noise level 2.
The rendering was stopped after 220 passes when the noise limit of 2% was measured.
Time: 41:38
Conclusions:
- Noise level is detected every X passes, where X is the "Adaptivity recalculation" setting available in Development / Experimental Stuff rollout (3ds Max | C4D). The default value of 5 should work well and there is no need to change it.
- Lowering the noise limit makes rendering longer, and image quality better, since more passes are calculated.
- To get 2 times less noise, roughly 4 times longer rendering time is required. 4 times less noise needs about 16 times longer rendering time, and so on...