Best way to render for compositing (greenscreen, etc?)

#1

What I’m aiming to do is render an animation of some trees and vegetation so they can be composited with a background movie. Essentially, the trees/vegetation will be Paint Effects plants with some wind motion, rendered on a transparent background, and this will be composited in the foreground of the finished clip to give a sense of wind movement, etc.

I’ve read everything I could find but I still feel there must be a ‘best practices’ way of doing this that I’m missing. Currently I’ve created a Green Screen plane, turned off most options in Render Stats, and set that to fill the background. I should be able to Chroma Key out the green in compositing, and I think it is workable, but it seems like such a hack to do it this way in a program like Maya.

Can someone point me to any information on the best way to do this, or just some instructions on what I need to set to ensure that I have a clean animation with good alpha channel transparency for compositing?
Thanks,
JT

#2

You don’t need to create a green screen for your render. The entire point of a green screen is to separate the stuff in front of it into a separate element, which is what a default render over black empty background in cg does.
Just render to a format that supports an alpha channel, practically anything but jpeg. Best is probably exr.

Edit: upon reading your post again, I see you are already aware of alpha channels, which begs the question why are you trying to create a cg green screen.
Are you having edge issues when compositing over your live plate?

#3

Thanks for the help, and I did resolve that it will all work as desired.

To answer your questions, and I was defaulting to making a green screen plane while still I looking for the right way to do this. Fwiw, when I render default settings in Maya with no background at all, the background renders to black. But, for some reason, with ‘realistic sun & sky’ lighting, the background renders white. The alpha channel is apparently still there, but the white bg can be confusing at first.

Fortunately, things seem to be handled well by compositing programs (Nuke or AE). In Photoshop, my tif image has the alpha channel turned off by default…or so it was for me. But when an image is brought into my compositing program, it seems to automatically note the alpha channel and selecting that as a straight mask will composite the foreground image(s) with transparency over the background.
Thanks,
JT