Caustics flickering (corona 12)

[markusmedk]

Hi!

I've been trying to render an animation of some caustics in pool water, noticing quite a lot of flickering as of Corona 12. I have tried changing the secondary solver to UHD Cache and 4K cache, both set to flicker free. I've also tried playing with the caustics surface multiplier making it less bright as well as a CoronaRaySwitch in the water material with no luck. I've read that a lot of people have similiar issues but with no fix. I also noticed the same issue with another animation of a glass - loads of flicker making the animation useless.

The water is a simple corona physical material with a phoenix ocean tex map connected to corona displacement modifier. I've also tried without the displacement modifier and connecting it into the displacement slot of the material. Caustics generated from a Corona Sun.

Rendered the same animation a couple of months ago with a simple noise map with Corona 11 without any issues, same settings.

I've read about the new and improved caustics as of Corona 12 using Markov Chain algorithm. But rendering 200 passes/frame for an animation is simply not an option.

[maru]

The UHD/4K Cache settings are irrelevant to caustics. It may not always be possible to render animations with caustics and acceptable time/quality.

The caustics solver uses a Markov Chain Monte Carlo algorithm, which means each frame in an animation (or even rendering the same frame twice) will have a different pattern in the noise. To avoid flickering in animations, you will have to render a significant number of passes to ensure the solution has converged.

Source: https://support.chaos.com/hc/en-us/articles/4954589213457

Having said that, feel free to send your scene over to https://support.chaos.com/hc/en-us/requests/new and we will investigate.

[RecentSpacesSam]

I'm surprised you say that UHD cache settings make no difference?

We've had great results increasing the UHD cache precision from 1.0 to 8.0 when rendering animations with caustics - although maybe this is no longer relevant on Corona 12?

[maru]

Do you mean that adjusting UHD precision made caustics flicker less? The directly generated reflective/refractive caustics are handled by the caustics solver (not UHD Cache). If caustics are so bright that they illuminate other objects, this also isn't handled by the UHD Cache.

If in some cases increasing UHD precision did affect caustics, could share renders/scene? I am just interested what exact scenario it was. :)

[Tom]

Hi,

Just jumping in this interesting conversation: I've been testing caustics animation with C11 with no particular flickering issue, even with a low number of passes. I used Path tracing for both solvers though. Did you try this option @RecentSpacesSam?

I read quite a lot of issues happening with Corona 12, this particular one about flickering caustics just being one more among others about slow loading/saving scene issues etc ... this really makes us reluctant to switch to Corona 12 (we're sticking to C11 at the moment).

I appreciate Corona but I'd be curious to hear from you guys at Chaos about what you honestly think of C12 and its related issues,if these issues are going to be addressed in C13, and if so, when (with the hope C13 won't bring new bugs/instability).

Thanks

[markusmedk]

Just jumping in this interesting conversation: I've been testing caustics animation with C11 with no particular flickering issue, even with a low number of passes. I used Path tracing for both solvers though. Did you try this option @RecentSpacesSam?

I rarely had any issues with caustics flickering in Corona 11 (mostly UHD as second solver). Haven't been able to get a flicker free animation of caustics in Corona 12 as of yet which is a shame considering the improved caustics in general.

It may not always be possible to render animations with caustics and acceptable time/quality.

Thanks for the reply. Do you think some workaround will be implemented in the future?

[maru]

Just jumping in this interesting conversation: I've been testing caustics animation with C11 with no particular flickering issue, even with a low number of passes. I used Path tracing for both solvers though. Did you try this option @RecentSpacesSam?

I rarely had any issues with caustics flickering in Corona 11 (mostly UHD as second solver). Haven't been able to get a flicker free animation of caustics in Corona 12 as of yet which is a shame considering the improved caustics in general.

We are not aware of any "regression" regarding caustics. They should render faster in Corona 12 compared to 11, but there shouldn't be any side-effect to this like flickering. If you have a scene which used to be flicker-free in Corona 11 but flickers now with Corona 12, please send it over at https://support.chaos.com/hc/en-us/requests/new
(or if you just have a scene which flickers in Corona 12)

It may not always be possible to render animations with caustics and acceptable time/quality.

Thanks for the reply. Do you think some workaround will be implemented in the future?

Sure, everything is possible in the future. :)