Particle flickering

[lukepenry]

I have a particle heavy scene, on smaller resolution tests i found it flickered, but assumed a higher resolution and smaller noise threshold would fix it when it comes to final rendrer, but i find no even at 1920x1080 0.01 noise thresh and 24 max subdivs it flickers on particles in the background. Is there a solution to this that won't increase render time?

Attached a video of the problem i'm facing.

https://www.dropbox.com/s/d6cj0azri7...ering.mp4?dl=0

Also i know i'm asking a lot of questions on the forums at the moment, but everyone is being very helpful, so thank you.

[Morbid Angel]

You probably didn't set the min subdivs to higher then 1? for small dots like that you need it to be quite high like 3-5 or maybe even 10 in some cases. The max subdivs is only good for smooth pixel transitions like glossy reflections or gi for example.

[lukepenry]

that works, thank you, had to increase it to 5, has impacted render time quite a bit though. but i guess that's life.

[Morbid Angel]

You have to think that a renderer is blind, in order for it to see anything it needs to shoot a ray. That's called 1 sample per pixel. For objects that are 1 pixel or few pixels in size shooting minimum one ray results often miss, though vray does a pretty good job of sampling them since you do see them, but it does miss some them frame to frame. Min subdivs essentially sends the sample rays more often to ensure it gets everything. I had shots where I had to set min subdivs to 20!

[lukepenry]

Oh wow, thanks for the explanation. So with that in mind, the output for my project is 8K, would that help stop the flicker even if it was set to something smaller, since the particles will be more than 1 pixel?

[Joelaff]

As a general rule higher resolution required less AA because there are more pixels. So, yes, it will help at lower res. You might have to go even higher at lower resolutions.

Tiny particles are where 2d type particles solutions shine because they can just draw every particle and not have to worry about raster sampling issues.

Also rendering techniques like drawing pixels for particles (like Krakatoa or I believe Phoenix particle shader in point mode) work well for small particles. Of course then the particles are all the same size and don’t change scale with distance to the camera.

There are always trade offs.