Corona Renderer Forum

Corona Renderer for 3ds Max => [Max] I need help! => Topic started by: etracer on 2021-09-16, 15:16:50

Title: Dancing Fireflies in Animation Reflections & Refractions
Post by: etracer on 2021-09-16, 15:16:50
With car materials or any kind of high IOR metallic material there seems to be a constant discrepancy around the calculation of the fireflies between animation frames, which results in 'dancing fireflies' as seen in the attached video file.

I've seem similar issues posted on the forums before but I am yet find a real solution for this issue & have so far tried many workarounds with varying success:

It has now happened across multiple files with different assets & lighting setups, also across bother Corona 6 & 7.

Any help or suggestions would be much appreciated.
Title: Re: Dancing Fireflies in Animation Reflections & Refractions
Post by: maru on 2021-09-16, 18:07:11
The frames seem to be rendered at a very low quality. You need many samples (longer render time) to efficiently sample a small light source far away from the reflective objects. I would suggest the following:

1) Letting the frames render for a longer time (I would say about 100 passes is usually the minimum).
and
2) Lowering the glossiness (or increasing the roughness) of the carpaint material just a tiny bit. For example, if it's currently 1, you can change it to 0.99. This should make it a bit easier to sample light reflections.
Title: Re: Dancing Fireflies in Animation Reflections & Refractions
Post by: aref3dsmax on 2021-09-16, 22:57:45
With car materials or any kind of high IOR metallic material there seems to be a constant discrepancy around the calculation of the fireflies between animation frames, which results in 'dancing fireflies' as seen in the attached video file.

I've seem similar issues posted on the forums before but I am yet find a real solution for this issue & have so far tried many workarounds with varying success:
  • Using UHD Cache (both clean and from file)
  • Increasing UHD Cache precision
  • Playing with GI vs AA Balance
  • Different Denoising Techniques
  • Dramatically reducing all reflections on materials in the scene (very unpreferable as reduces scene quality)
  • Turning off light visibility in both reflections & refractions (again very unpreferable as reduces scene quality)

It has now happened across multiple files with different assets & lighting setups, also across bother Corona 6 & 7.

Any help or suggestions would be much appreciated.

use Highlight
Title: Re: Dancing Fireflies in Animation Reflections & Refractions
Post by: etracer on 2021-09-20, 13:48:00
Thanks for your responses.

Maru, unfortunately I found neither of those solutions to have worked. 
1) Even with the longer frame render times the difference in the fireflies was just as exaggerated.
2) Fractionally reduced glossiness has already been applied to the scene, for this process to work I found it needs to be considerably lower than 0.9 to reduce the fireflies but that also damages the overall quality of the materialisation. 

aref3dsmax, on the other hand ive found your solution to work pretty well!  With some experimentation of different clamping values and alterations to the post processing I've been able to achieve the desired result without effecting the over all scene.   I feel I initially overlooked the highlight clamping settings and assumed they were for compression. 

Thank you both again for your input and would recommend the Highlight clamping solution to any one else having this issue.
Title: Re: Dancing Fireflies in Animation Reflections & Refractions
Post by: maru on 2021-09-20, 17:21:51
Just remember that highlight clamping disables high dynamic range in your output, for example if you are planning to save your frames into a 32-bit format. See: https://coronarenderer.freshdesk.com/support/solutions/articles/12000006462-what-is-highlight-clamping-