Noisy reflection passes through windows with vraysky or other light intense objects as backdrop

[chromaloma]

I noticed that the VrayReflection and VrayRawReflection passes in my interior scene gets way too noisy in windows where VraySky is the backdrop. Very unsuitable for compositing. See attachment noise_sky.jpg.
To solve this, I tried placing a plane with a default VrayMtl to cover that backdrop area behind the windows, and voila the noise was gone.

Now, this plane was showing its shadow side, so it had low light intensity. To test further, I tried introducing a light on this backdrop plane to crank up its pixel values, and it seems like the reflection pass gets incredibly noisy as soon as there are some values on the backdrop that goes above 1, 1, 1.
Are there any mechanisms here in play, and what can be done to avoid this noisy behavior? More often than not, a window background on interior scenes is naturally burnt out. While in the real world you would photograph two or more exposures, but for practical comp matters in the 3d world it would be sometimes handy to not have to render a second exposure for just adding back those reflections after adding a scenery backdrop.

Let me know if you have any tips here, but for me as it stands, it seems like an issue.


Thanks

[vladimir_krastev]

Hi, thanks for posting. Could you send us a scene that reproduces this issue? You can do that here or through the support contact form. If you use the contact form, please add a link to this thread in your e-mail.

[chromaloma]

Done. Let me know your findings, thanks.