Reflected caustics on building

[KamilR]

Hi guys!
I have a problem with water caustics. As you can see in the attachment there is so much noise on the building facade, but on the L-shaped plane in front of the rendering, the water caustics are clearly visible - noisy, but at least it is possible to see caustics drawing. In the background, on building facade there are just white, big noise dots which are unacceptable in final render :(

Some informations about scene:
- sun&sky light
- default render settings
- basic water material + noise connected (bump) - screen in attachment
- bacic coronaMTL on building facade - correct abledo value

I have tried everything. Noise connected to bump, displacement, creating 3d noise with basic water material (no bump mapping) without any good result. The L-shaped plane in front of the image is just for test - will be deleted anyway.

Thanks for any suggestions!

[romullus]

I think if you'd move the test plane to the same position where the building's wall is, you would get the same result - too noisy caustics. The reason is the distance from the water surface. Caustics are not laser - with distance they get more blurry and probably at some point there is not enough photons emmited to converge to meaningful solution. I would try to play with caustics settings, but i can't give you more specific advice here.

[KamilR]

What do you mean excatly? To play with connected noise bump map? In render settings there is just "enable/disable".

[romullus]

I don't have Corona now, but IIRC when you enable caustics solver, there should appear caustics settings rollout in performance tab (or maybe you should enable it in dev/experimental rollout). Hopefully someone from support team will tune in and will guide you further.

[maru]

Which version of Corona is this? There were some improvements in V6 dailies if you would be willing to try that - https://coronarenderer.freshdesk.com/support/solutions/articles/5000570015-corona-renderer-for-3ds-max-daily-builds
Other than that, could you share the scene with us? We could then try to optimize it / see what the issue might be.
Uploader: https://corona-renderer.com/upload

[KamilR]

It's Corona 5, 3DsMax 2019. I've uploaded the file :) I hope there will be some good news!

edit: filename - Successfully uploaded as 1594741487_caustics-scene.zip

[maru]

Here are some experiments:
note1: I lowered the resolution but the improvement should be independent from that
note2: all images were rendered with 3 min time limit on a Ryzen 3900X

- reset render settings (I only did it to have a "fresh start") - render setup > scene > reset settings
- enable caustics in the Performance tab
- disable "Generate caustics from environment" in Performance tab - since we mostly care about the caustics from sun
- set GI vs AA to 8 - caustics are calculated between each pass and lowering this allows more passes to be rendered within the given time = more caustics re-calculations
- set light samples multiplier to 1 - this does not lower the quality in this case and makes rendering slightly faster
- set Max sample intensity to 10 - again, small speed up and no visible bias

- experimentally changed water material's reflection and refraction glossiness to 0,99 - this makes the caustics a bit more smooth, but also blurs the refraction and makes reflections darker - optional

- experimentally re-rendered in 07.07 V6 daily build - virtually no visual difference in this case

- experimentally enabled development/experimental stuff rollout (https://coronarenderer.freshdesk.com/support/solutions/articles/12000021288) and increased the number of caustics max photon / iteration from the default 5 000 to 25 000 - note that this will always improve caustics quality, but will also make rendering globally slower and may cause running out of RAM

I am attaching an archive with all renders here. I hope that helps!

Pozdrawiam,
Marcin :)