How can I tell whether noise comes from direct or indirect light?


The easiest way to find out whether the noise visible in your rendering comes from direct or indirect (GI) light is to add CESSENTIAL_Direct and CESSENTIAL_Indirect render elements. 

To do this, go to Render Setup > Render Elements > Render Elements rollout and press the "Add..." button. Pick CESSENTIAL_Direct and press ok, then repeat the same process with CESSENTIAL_Indirect element. Upon doing this, you will be able to see the selected render elements on the roll-out menu in Corona's VFB during rendering.


  • If you can see that there is more noise visible in the CESSENTIAL_Direct pass:
    This might suggest that your scene needs more direct light samples. To add more direct light samples, go to Render Setup > Performance > Performance Settings > Sampling balance and slightly increase "Light samples multiplier". The default value is 2, and it is not advised to increase this value above 4. 


  • If you can see that there is more noise visible in the CESSENTIAL_Indirect pass:
    This might suggest that your scene needs more GI samples. To add more GI samples, go toRender Setup > Performance > Performance Settings > Sampling balance and slightly increase "GI vs. AA balance". The default value is 16, and it is not advised to increase this value above 64.


Note: Total amount of samples is dependent on "Light samples multiplier" and "GI vs. AA balance" values. If "Light samples multiplier" is set to 1 and "GI vs. AA balance" is set to 16, this means that 16 GI samples and 16 direct light samples will be used for each pixel per pass. If "Light samples multiplier" is set to 2 and "GI vs. AA balance" is set to 16, this means that 16 GI samples and 32 direct light samples will be used for each pixel per pass. In some situations it may pay off to reduce one of these values and increase the second one, or even to reduce both. Typically, there is no need to increase "GI vs. AA balance" above 64 and "Light samples multiplier" above 4.

See: Light samples multiplier

See: GI vs. AA balance

Read more about getting rid of excessive noise here.




Examples


Noise is visible in the direct light (CEssential_direct pass).

After 16 passes there is still visible noise in direct light. If it persists, this may suggest that more direct light samples are required to efficiently render the image.



Noise is visible in the indirect light (CEssential_indirect pass).

After 16 passes there is visible noise in indirect light. If it persists, this may suggest that more GI samples are required to efficiently render the image.