foam flickering - beer animation

[Svetlin.Nikolov]

Hey,

Sorry for the delay, been playing with the render settings of the later frames. So it seems like the most important settings for this problem are:
- Render in cellular mode. Definitely render in cellular mode. Otherwise a pair of bubbles would appear with one bubble completely in front of another in one frame and completely behind on the next frame once its center goes behind the other bubble's center. This would cause abrupt changes in the overall look of the foam mass in animation.
- Turn Optimize Congestion off - it's highly recommended to have it enabled as it is by default, but since disabling it does not affect the performance significantly, this would allow bubbles to not be removed from the rendering if they happen to be fully enclosed by other bubbles or very near other bubbles. This would also help get rid of flickering or noise since bubbles won't disappear and re-appear in animation.
- Do not animate the Threshold or the Count multiplier - same reason as above regarding bubbles disappearing or appearing out of nowhere.
- Lowering the Light Cache Speedup will help highlights on the bubbles jitter less with complex lighting.
- Increasing the Bounces will help the illumination over the bubbles in a large bubble mass be more consistent in animation - otherwise with a lower Bounce number, each bubble will be affected only by the near neighbors and when they move around.
- The reflection cut off should not be too high.

- You might also wanna try disabling Probabilistic Shading from the Phoenix Atmosphere - this is good when rendering using V-Ray Progressive, but might be slower for bucket renders.

- Finally, I gotta find the issue that's causing Glass Geometry to cause different results using different number of threads. I have to check it further, but it's possible that it might also cause slightly different results each time you render the same frame, so this might also be causing some flicker.

[jgreen3895]

Svetlin,

Thanks you so much for this information. I will give this a shot first chance I get and let you know how it goes.

Cheers!

[jgreen3895]

Hello,

I've been experimenting with some new settings and the results are getting better. I've switched to cellular mode, disabled optimize congestion, and reduced reflection cutoff to .05. I've also increased the bounces to 10 and decreased light cache speedup to as low as .01. Bounces and Light Cache Speedup seem to have the most to do with flickering, but also greatly effect render time.

Unfortunately, even with these adjustments there is still some flickering occurring. I imagine that if I lowered light cache speedup even more and perhaps raised bounces as well I may be able to finally get rid of the flickering, but the problem is that render times have already increased dramatically. The count multiplier in my setting is set to 1, as opposed to .5 like in the previous post, but even at .5 the render time is very high still and for the look I'm going for 1 is really best.

It seems like in order to get flicker free animations in such a dense foam area like the top of the beer, the only solution is to accept the fact that render times are going to be quite long due to the light cache speedup and bounces settings.

One thing I haven't really tried is using a different light source. The HDRI map on the dome light may be what's requiring such drastic settings to avoid flickering. Not sure though.

I'm on the verge of giving this project up, but I'll still be welcoming any potential suggestions if you have them.

Thanks!

[jgreen3895]

I do have a question though. Regarding the nightly updates, is there a specific place where each time there is an update there are some details about what's been updated. If so, could someone please provide a link to that.

Thanks!

[Svetlin.Nikolov]

Hey,

Asking just in case so we are on the same page - what currently occurs in my tests is that there is noise in the bubbles above the liquid. Can we confirm that there is no more flickering in the early frames of the bubbles under the liquid?

Indeed, decreasing the speedup and increasing the number of bounces will reduce the remaining noise further at the expense of render speed. Also, from our tests, it seems like removing the HDRI or replacing it with a different map that represents less light sources is the main contributor to the flicker, jitter and noise effects once the animated count multiplier, threshold, cellular and optimize congestion are adjusted. Please note that in order for the foam to render at all in reasonable time, all these cheats such as the light cache and the bounces control are applied in order to approximate the lighting at the expense of some other features. E.g. when using the light cache, the illumination over a bubble is the same over its entire surface, so if a few other bubbles should cast shadows over it, finally the bubble would be either entirely in shadow, or entirely illuminated when light cache is used. Such shortcuts finally add up to the result you are getting.

Also, note that I still haven't fixed the issues where the lighting is not always the same when Glass is on - however, you can see if this would improve the rendering right now - if you turn it off and you still get flickering, then this is not going to contribute anyway when fixed.

You can render the bubbles as real physical refractive spheres e.g. using an instancer just for comparison, but I strongly suggest that you try to re-organize the way the scene is lit instead.

You can check what changes are in the nightlies in the "release_notes_XXXXX.zip" file - there is a changelog there with more info that a regular release log, so hopefully it helps

Cheers!

[jgreen3895]

Hey,

So there is definitely still flickering in the bubbles above the liquid most likely due to the settings and the specific HDRI light source that is being used. Also the density and amount of bubbles as well. At some point I will likely go back and try with a new HDRI map with less light sources or maybe just try creating a lighting setup using standard rectangular lights instead to see if I can get better results because it seems that with my current HDRI map, the only way to avoid the flickering is to use settings that would cause extremely long render times.

As for the bubbles inside the liquid, I haven't tested this yet using any of the new settings or latest nightly build. The flickering that was occurring with these bubbles though seemed to be a different type of flickering. Basically the bubbles were disappearing and then re-appearing as opposed to "flickering" that would be caused by highlights and things like that. I believe this issue was due to the render farm and the use of multiple nodes because that flickering that was occurring beneath the liquid wasn't occurring during the local tests I ran back when this all started. And when I tested some of the problematic frames locally the results were correct.