Caustics Flickering in animation

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Hello,

I am trying to render the animation of an aerial camera but caustics are giving me a pretty nasty flickering as you can see in the attached GIF.



Water's waves are made with PhoenixFD (Ocean Texmap as Displacement) and they are animated. I am using Corona 6 (Hotfix 2) as I didn't have the time to jump to Corona 7 yet. Also I use 3ds max 2020

The result in the GIF came out with UHD Cache (load from file) option and although I have tried:
a) To calculate it for every frame.
b) To use Path Tracing as the secondary solver
c) To use 4K Cache, both with load from file or calculate it for every frame

I haven't found the solution yet. 4K Cache and Path Tracing helps a bit the situation but still the flickering is visible.
Displacement for the whole of the scene is set to World size 1cm except the stonewalls which are set to 0.7cm for cleaner results.

Any idea?

Thank you!
Christos

[maru]

This is currently expected and a possible solution is rendering for a longer time (=more passes).

The new caustics use 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.corona-renderer.com/hc/en-us/articles/4402402468753

Another option would be enabling the development/experimental stuff rollout ( https://support.corona-renderer.com/hc/en-us/articles/4402367677713 ) and then going to Performance > Caustics Solver and increasing the number of photons from the default 5 000 to a higher value (e.g. 15 000 or maybe even 20 000). Using too high values will make you run out of RAM though.

Another option would be using some kind of 2D editing software that can deal with frame-to-frame flickering (deflicker with temporal consistency).

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Hello Maru,

The only thing is not clear is that part about the "pattern in the noise". Is this true also about PhoenixFD ocean tex or it talks only for old classic Max's noise? The ocean tex has an animation of moving forward by time, so indeed the "noise pattern" is different on each frame but it is correlated to the previous, not so different, noise pattern.

Essentially, I did what Recent Spaces did. I wonder if they had this issue.

Thank you

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Also... I just face a stupid problem.
It looks like if you enable and disable devel/debug mode twice, another panel on performance shows up called "Bidirectional Pathtracing/VCM Render Engine" which I cannot hide somehow and it has made "Caustics solver" panel unavailable...help!

Nevermind, I found it out