Strange GI behaviour through relfections

[masterzone]

Hello to all,

recently updated Cinema4D to 2024 and Corona 10 latest release.
Today I'm starting a new project for a client of mine, and I noticed a strange behaviour of the curtain (with translucency turned on) and the mirror...as you can see there are many splotch on the reflected one...the curtain has two surface due to a roll curtain shape...so I have two surfaces with the same material.
The problem is gone if I turn off one of them...
Ideas?

[Beanzvision]

Hi,

I am not able to reproduce it here. Is this a final render or IR? If IR, is denoising enabled at all? Having the scene would be best. If you can strip it back to just the room and share it with us, that would be great.

[masterzone]

Sure..I can share the scene too... (give me a little bit) if you have the scene opened, could you try to copy the same panel for the curtain and put it a little bit far from the previous one? 5 cm of distance between...
Alex 💪🏻

about your questions: it happens on IR and final render too, but into the final render the splotches are more little...denoise is turned off...

EDIT: did you tried to zoom into the image? try to zoom near the divider of the windows and see the differences, you can notify a bad quality on the mirror...here is not a problem but try to duplicate the curtain...

[Beanzvision]

Grr, my C4D just froze and I had to force quit it and lost my scene. :/ I will wait for yours if that is ok?

[masterzone]

oh no...don't say into the forum...😂

anyway, here the link for the scene:

www.c4dzone.com/clienti/test%20room.zip

[romullus]

I would try to increase UHD precision, or even switch to PT+PT, although that would lead to longer render time.

[masterzone]

The UHD is very suitable for interiors rendering instead of PT. I think is the UHD splotch as well...the strange behaviour is the low quality on reflections surfaces...
:)

[pokoy]

Did you try with the 4K cache instead of UHD?

[masterzone]

just now, the quality is better than UHD standard...some little splotch on the corner but is good on the surface...

[Beanzvision]

So the problem seems to be somewhere in the render settings. I copied the entire scene to a new one and it now renders as expected. I also deleted the phong tag from the mirror as it distorts the reflection. I hope this helps.

[masterzone]

mmm...interesing...I didn't try to copy and paste the scene in a new one...I do many time when something goes wrong but not now...
I created the scene on C4D 2023 and today morning I upgraded to 2024 and corona 10...but I created only the models without rendering or Corona...so It's very strange...
thanks
Alex

[Beanzvision]

Glad I could help ;)

[masterzone]

thanks for for your time!

[maru]

This is a known issue which may appear under certain circumstances, for example when using slightly glossy reflections/refractions.
What should work is enabling the "animation" preset for the UHD Cache.
More on the UHD Cache: https://support.chaos.com/hc/en-us/articles/4528607789585

Internal info - some reports which mention similar issues:
(Internal ID=294016924)
(Internal ID=321530570)
(Internal ID=568651148)
(Internal ID=205122297)

[masterzone]

thanks...