Corona 1.4 & Caustic

[burnin]

Very nice results.

Does it work in C4D version? Is engine on pair?

@giona4
What do you use for edges (modeling, shader...)?
Looking good.

Here's simple scene test, rendered with BD/VCM (BD-PM option is not available), caustics for material on, lighting sun+sky only, water surface displaced. Resulted in fireflies and much darker refraction than w/o caustics. Should report a bug?

Edit/Note:
Done with Corona for Cinema 4D Alpha version: A6 daily Jun  2 2016 (core 1.4 DailyBuild Feb 11 2016) - reported on Mantis (ID 1984)

[FrostKiwi]

I ran a caustic test scene and looked at how the Rays are being distributed.
The SamplingFocus render element is normalized to 0-255 in the attachment.

Caustics hitting the Floor had on average a realRGB of ~1.25 with the highest couple being ~2.
Caustics as seen through a refraction had on average a realRGB of ~3.5 with the highest couple being 7.

Adaptivity samples caustics through refraction more than twice as often as not seen through a refraction.
While it is correct to assume, that adding refraction makes the chance of a Ray spazzing out a random color and creating noise, it is the exact opposite in this case.
The most noise was produced from the caustic rays on the floor being scattered across the Plane. They created the most visible noise, (partly due to the fact, that the floor had a solid color and thus makes noise more visible) yet still was sampled only half as often, as caustics as seen through a refraction, which did not contribute to the Subjective Noise as much.

Kinda like the Mantis post I made, where glossy reflection of a glossy reflection was sampled twice as much (which didn't produce much noise) vs the first bounce of GI, (which produced the most amount of noise), yet was sampled only a quarter as much as the average of the whole image.

edit:
Scene was rendered in Progressive with 1250 passes and 0 MSI.

[Radim Razzak]

Hello everybody,

This might be a really stupid question, but how can I enable this Experimental section in the Performance tab? It looks like it's hidden from the casual users too well. :)

Thank you

[TomG]

Hidden with reason :)

In 1.5, you can find it by enabling the Devel/Debug mode - go to System tab, System Settings button, check Enable devel/debug mode, close the menu and head on over to the Performance tab.

[Radim Razzak]

Hidden with reason :)

In 1.5, you can find it by enabling the Devel/Debug mode - go to System tab, System Settings button, check Enable devel/debug mode, close the menu and head on over to the Performance tab.

Great, thank you very much!

[Radim Razzak]

Well, after having followed the hints and tricks mentioned above, I managed to get some caustics in my test render. But the bad news is that I get these white artifacts even after 3 hours of rendering on my dual xeon. Any idea on how I could get rid of these or what might be causing them? I just used a simple HDRI setup for fhe lighting.

Thank you.

[FrostKiwi]

Well, after having followed the hints and tricks mentioned above, I managed to get some caustics in my test render. But the bad news is that I get these white artifacts even after 3 hours of rendering on my dual xeon. Any idea on how I could get rid of these or what might be causing them? I just used a simple HDRI setup for fhe lighting.

Thank you.

No easy solution this time. It's an experimental render engine, that is ultra naive.
Sampling into a pixels works by averaging the cast sample with the previous result. A reflective ray with a >255 energy will take days to average out against the only 128 blue. These are extreme fireflies.
This is usually solved by blocking rays from having high energy with the MSI option. Problem is, that BiDir doesn't honor that option and Caustics are by definition high energy rays and thus you can't really use that option.

So you have to do it manually in post. You may be lucky to be able to just crush that information inside the Corona VFB, by looking at the intensity of the firefly with right click and setting Highlight compression to roughly the roughly same amount + some more to get it under white.

But most likely that will look aweful, use Corona's built in firefly filter option.
or
Export as any HDR format.
Either:
Go into Photoshop and try Median Filter with 1px or 2px amount, or
Use any firefly filter like ArionFX's Despeckle, or
Use Burntool to paint the Fireflies to 0-255 range by hand.

edit:
Remove Outliers filter in ImageJ worked wonderfully.
(I'm sure you can find many other tools, currently programming with it, so had it on my desktop :D)
Free tool, can download it here.

[Radim Razzak]

Thank you very much SairesArt!