Corona Flickering Problem

[BigAl3D]

MacOS 10.12.4
Version: 4 hotfix 3 (core 4 (Hotfix 3))
Cinema version: R20.059 CINEMA 4D Studio (single-license)

OK so this has always been a problem with Corona whenever there are very reflective materials. The first time for me was a chrome material. After posting the scene, the devs said my settings for the chome were "crazy." So ever since, we've been using the formula the devs suggested. For reference, I uploaded this scene to the private uploader yesterday concerning crashing issues. Please see the file:  Crash_SceneFiles.zip

Here's the test that's behind this almost black image. This is a single frame of an animation. Rendered twice on the same machine. I stacked them in Photoshop and told the upper layer to use the mode Difference. This will show only the pixels that are different from each frame. In a perfect world this would be solid black as they are the exact same scene, at the exact same time, rendered on the exact same PC. This example is using 30 passes full denoise. WHY are these two frames different? Do the rays being shot into my scene equate to a simulation, where each moment in time could be different each time I render?

I'm also attaching an animated GIF that I hope you can see the flickering well enough. There is a little dancing noise, but it's those bright pixels that appear and disappear randomly and the denoiser doesn't touch them. This animated example was rendered with 100 passes. This reduced some of the flicker, but still way too much for an animation. These cars will slowly rotate so it will be easy to see the flaws.

Also, this Vimeo link show my first render attempt. Maybe only 16 passes, you it really shows the flickering. (can never get Vimeo links to work on these forums for some reason)
vimeo-dot-com  /362894380

[TomG]

Yes, casting rays into a scene does by nature involve a bit of randomness, which means things may not be identical on each render.

May be best to upload the scene as hard to tell what is happening there - could be the lights are very small, could be some material settings, would be interesting to know if those pixels are in the Reflections pass or somewhere else, would be good to see what filtering was being used, what the bloom&glare settings are, what denoiser was being used, if any sharpen-blur was used, and so on. See https://help.c4d.corona-renderer.com/support/solutions/articles/12000033461-how-to-report-issues-c4d for the links to the private uploader etc.

[jojorender]

Hi BigAl3D,
this kind of flicker reminds me of what I see when rendering animations with trees, grass etc.
While turning down gloss in leaf material helped a bit, what ultimately worked for me was romullus tip of doubling render resolution.
Thanks romullus!!!

Video (or picture) has limited resolution and when very thin object is travelling through screen, it may occupy different number of pixel lines. In one frame it might be displayed as two full lines and in the next one it might be smeared over three lines. The thinner the object is, the more pronounced shimmering will be. Better filtering algorithm may help to reduce the effect, but ultimately, in extreme cases like yours, there's only so much it can do. Rendering at bigger resolution, would be the best option here, because it would affect the root of the problem. If you were using time limit for your animation, then i'd suggest to leave time limit the same and double the resolution - rendered image will be much noisier, but when you'll downsample to half rez, it should contain roughly the same noise level as original frames, but AA will be much better. You can also use blurrier image filtering with bigger radius, because downsampling will make your picture much sharper and generally you don't want too much sharpness in animation.

See this thread https://forum.corona-renderer.com/index.php?topic=26131.msg155842#msg155842

Maybe give that a try and let us know how it works in your case.

[maru]

How many passes did you render?

I would suggest lowering the GI vs AA number (from the default 16 to 8 and if that does not help, then to 4, but not lower) and allowing Corona to render more passes.

[BigAl3D]

@TomG Yes, I did upload the scene file. I referenced it in my original post. It was uploaded as part of another thread about crashes, "Crash_SceneFiles.zip" but I figured you can use it here as well.

@Jojorender and @maru We are in full test mode right now and will implement all your suggestions and post back with the results. Thanks for the input.