FG is always blamed for flickering animation and in this tutorial I'm going to share some tips about how to get flicker-free FG animation with mental ray in 3ds Max. I'll be using one of the production scenes from my latest project to demonstrate this, as it contains a large amount of polys.

So let's start with this snowy airport scene. I have enough RAM that I can render out entire scenes. The whole scene is lit with single skylight and sky texture as an environment. I also have an Environment/Background Switcher map loaded in environment slot and have used a sky Arch: Env blur shader inside the environment slot of the Switcher map. That's about it for the lighting, which is simple. Now let's talk about FG (Fig.01).


In this scene, everything is still and just the camera is moving around, so I chose Project Points Along Camera Path (as the camera is moving) and Single file mode (as everything is still and there's no animation). Also FG Bounce was set to 1 and I kepy Trace Depth to 2-1-1. I didn't need much reflection or refraction here. Noise filtering was set to None (Fig.02) and, of course, Antialiasing was set to 1-16 high settings with 0.05 default Spatial Contrast and Mitchell Filter.


So I generated a FG map for every fifth frame (for 50 frames), then locked it and rendered with those AA settings and here is the result (watch in full screen with HD on) (Fig.03).


As we can see, it's flickering there. But wait, it's not FG flickering. How do we know that? There are diagnostic tools in mental ray. Go to Diagnostic tools and enable Final Gather and now render out the sequence with that enabled. The result will be like Fig.04. As we can see, all those green dots aren't moving or jumping but sticking to planes and ground (watch in full screen with HD on).



So what is the flickering then? It's antialiasing flickering. It's always antialiasing flickering not FG. FG doesn't flicker if the correct settings are chosen. Let's enable Sampling Rate and disable Final Gather in Diagnostic tools, and render out the sequence. Here is the result (watch in full screen with HD on)(Fig.05).