You can use the noise level limit to stop Corona's progressive rendering once the specified noise level is reached. The noise level limit is available only if adaptivity is enabled (it 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.
The noise level is re-evaluated every X passes, where X is the "Adaptivity recalculation" value available in the Development / Experimental Stuff rollout ( 3ds Max | C4D ). The default interval should work well and there is no need to ever 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 when the noise limit of 17,22% was measured.
Time: 01:06
2. Noise level 10.
The rendering was stopped after 10 passes when the noise limit of 10,97% was measured.
Time: 01:49
3. Noise level 5.
The rendering was stopped after 35 passes when the noise limit of 5,61% was measured.
Time: 05:25
3. Noise level 3.
The rendering was stopped after 95 passes when the noise limit of 3.3% was measured.
Time: 16:01
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 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...