weird flickering in metaballs

[Jassir]

Hi there,

I have some weird flickering in a phoenix simulation that I rendered using vray metaballs. I uploaded a short video that describes my problem:

https://youtu.be/KFpajVb-fqs

The flickering is somehow dependent on the camera distance. It is almost completely gone from one frame to another when tha camera moves closer.
I used phoenix to produce a sand or grain like behavior and vray metaballs to render individual particles. I know that it is not perfect but I would be happy with the result were it not for that flickering.
I tried different values for the metaballs, render and motionblur settings. But I didn't find the right combination yet. Any ideas???

Here are the settings I used for the sequence above.


Rendered in FullHD and I increased the motionblur samples on the metaballs object from the standard 2 to 8.

I have no idea what I am doing wrong. Any help would be much appreciated.

[Zdravko.Keremidchiev]

This seems like an GI issue, does it still flickers if you use BF+LC or BF+BF?

[Jassir]

Hi,

thank you for the reply and I am sorry for the late response. I tried your suggestion and it is better now but still visible. I uploaded a new preview, I left the settings as they were before and just changed GI to BF+BF with 3 bounces.

https://youtu.be/ay88FEtFoeI

Is there something else I could try?

[svetlozar.draganov]

Would it be possible to send us the scene with a few cache files of the frames that flickers the most?
FTP could be provided if needed, just let us know.

[svetlozar.draganov]

We just completed the test here and we managed to replicate the issue.
We've noticed that you are using a Motion Blur effect in the scene but the the same time the Velocity has been turned off in the Output options of Phoenix FD simulator:

That setup is not proper because the motion blur effect needs to know the velocity information from the simulator.
Right now it only has a velocity information from the backup frames and those are the ones that are rendered properly and also that cause the flickering.

Please turn the Velocity on, re-simulate the frames, re-render them and let us know if that resolves the flickering or not.

[Jassir]

thank you for looking into this. Maybe I should have added one piece of information from the beginning. I simulated in a second scene. I used the scene I sent you only for rendering purposes. The settings of the Phoenix simulator in the render scene don`t match the settings of the simulator from the simulation scene (do they have to match?). I just added a simulator in the right position and set the input path to the cache files from the simulation scene.

Here is a screenshot with the simulator settings of the simulation scene.


You can see that I had ?velocity? checked. In the ?cache file content? box there are values for velocity as well, but I don?t know if they are the same or if they look right.

I rendered the sequenz again, this time with motion blur disabled. That way motion blur can not be responsible I think.
The original problem still happens. Without motion blur you can even make out a line where the image becomes brighter. Here are three consecutive frames of this sequenze. The first one is darker, in the middle one you can see the line and in the last one everything is a bit brighter.

[svetlozar.draganov]

Thank you very much for the additional details, it looks like this is a bug after all.
The case has been added into our bug-tracking system and will be investigated further by our developers.
We'll keep you posted for any updates.