Indirect reflection noise

[Neon Junkyard]

So this might be a question of mantra settings in general but I am having problems getting rid of indirect reflection noise, it seems like no matter how high my settings this pass is coming out extremely noisy and it is showing up in the final render.  I have read through all the docs regarding noise and read through the forums but since mantra changes with every release I don't know what information is still relevant.  For instance I read the practical upper limit for pixel samples was 6x6 unless you have heavy DOF or motion blur.  I have no idea what extreme settings would be for anything else though like sampling quality on lights or min/max pixel samples.  The docs say in some cases you have to increase min ray samples for indirect reflection/refraction noise, but I read elsewhere not to increase that. What is the workflow there, when should this be increased? And how does that affect reflection/refraction quality, which seems to be a global multiplier?  Also on the noise removal docs it says as an example 100 max indirect ray samples to achieve a clean image, is that referring to "enable indirect sample limits" rendering parameter on a shader? Is there not a more global way to set that or is that what sampling quality on each light is doing? However increasing that per light doesn't seem to make any difference.  

I should mention I come from a vray background so that is the workflow I am used to, if anyone can draw any parallels.  Also this actual scene doesn't really matter, these are more general questions about newer mantra settings and when to tweak what

 

Quick info about my scene-

Still image, no DOF or motion blur, no environment light, just 3 area lights with sampling quality of 9

I do have some fine displacement which might be part of the issue, set shading quality to 3 on that object.  Here are my render settings (refl and refr limit at 5, no diffuse bounces, color limit 5).  Everything else is default

Indirect reflection pass-

Here is the comp zoomed in a bit, you can see there is visible noise on the black spheres and the displacement, there is also some square artifacting happening, my guess is the displacement is just too fine for mantra to dice properly resulting in a moire pattern type of effect but that wouldn't explain the square artifacting (that is in the raw exr, is not jpg artifacting) 

 

 

Any help on this would be greatly appreciated

 

 

 

 

[acey195]

not a rendering person myself, but yeah to me it seems you need more rays to make sure the entire area is covered (like with caustics)

If that would cost too much performance, you may want to lower the reflective bounces (200 rays * 3 bounces) or (120 rays * 5 bounces)
To be honest I'm not 100% sure that is how the math works, but that would make sense to me at least...

[DaJuice]

Just at a glance I would say increase Reflection Quality and/or crank up your Max Ray Samples. Your Noise Level is pretty low, but that doesn't do much good if your Max Ray Samples are capped at the default value. I do believe the docs are up-to-date regarding Mantra and they go into some detail about combating specific types of noise. The direct reflections of your lights look pretty clean so maybe you can ease off the Sampling Quality on those.

Not sure about the displacements or artifacts. Are you using a material that has the displace bound parameter? If you think it's a dicing issue you could always increase the Shading Quality and see if that helps.