Hi, here are my initial observations. They may not be 100% accurate. :)
Post 1 - Reflective caustics (HDRI lighting falls onto the metal, then this is reflected onto the non-reflective surface). You see "splotches" because various shapes from the HDRI are producing various intensities on the surface. It goes away when MSI is lowered, because then light bounce intensity is capped.
Post 2 - We don't know how fstorm works internally, but it is possible that it uses heavy clamping or does not produce GI from glossy reflections (these are just guesses). So it is missing the effect that happens in real life and is visible in Corona.
Post 3 - Exactly the same comment as to Post 2.
Post 4 - Same.
Post 5 -
https://forum.corona-renderer.com/index.php?topic=41005.msg217107#msg217107 - this one is interesting. I have two questions about it:
- Are the inconsistently splotchy patterns reproducible if you switch from Path Tracing + UHD Cache to Path Tracing + Path Tracing?
- Are you using some kind of denoising?
I am asking because both the UHD Cache and denoising can produce varying splotchiness. The UHD Cache takes care of GI and also affects glossy surfaces, so it may be related. Switching to PT+PT would remove UHD from the equation.
Update: it could also make sense to add CESSENTIAL render elements and see where those splotches appear.
Update 2: attaching a similar scene from Max 2024 and 3 renders (no changes, just hit render 3 times). It's a non-reflective ball and a reflective floor + 3 Corona lights with high directionality. You can see the changing pattern. This is caused by the UHD Cache "splotches". The solution would be to switch to PT+PT, or possibly the "animation" preset of UHD Cache may help.
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