3d shadows question

[kene555]

I use Bryce 6 for my 3D animation. To use it in my videos, I put a blue background behind the 3D subject, and use Keylight in After Effects 6.5 Pro. How can I put a 3D object in my video, and also give it a shadow. Like, for example, if I import a video of a spaceship made in Bryce, how can I put a shadow that will transfer over to the video as well? Or is this not possible?

[Firestorm]

I know in 3DS there's a certain kind of preset material like "shadow matte" or something that you can apply to an object to make it transparent except for the shadows it receives. You might not want to use a blue background for that though and instand render to something that supports alpha channels (PNG sequence for instance). The material thing might be the same for Bryce.

[MasterMike]

Create a false surface upon which to cast your shadow, then when you export make sure that only the shadow is rendered, not the surface itself, and export as something with a premultiplied alpha option such as PNG, TIF or EXR.

[Grant]

Would it not be easier to imprt the video in theh 3D program, include the objects/shadows and then export the entire sequence

[MasterMike]

Often, no - you're much more at liberty to tweak your 3D rendering's colours, highlights, blur match, film grain etc in a compositing package. I'd only use the video as a reference in the 3D package, rather than exporting with the video as a background.

[kene555]

thanks for the tips.

i was able to figure out how to solve this issue. i made the sky a pure blue, and created a flat ground the same pure blue as the sky. you are unable to see the difference between ground and sky, and a shadow is apparent. thanks for your help

how i normally did 3D bluescreen: no ground, sky preset to deepest blue

ground layer added with same color as sky

[MasterMike]

Good work. I really would implore you to start using a pre-multiplied alpha format instead of a blue background, you'll get perfect edges without an additional keying job.

[kene555]

The only choice I have for exporting animations as video is .avi

otherwise, i would definitely export as an alpha channel