Video questions

Kodiak3d

I'm trying to blend live action video with a background rendered in Carrara.  I want to find a way to use the live video (against a greenscreen) to cast shadows on the Carrara background.  I've gotten as far as having a plane in Carrara with the video as a texture with the greenscreen removed via the alpha channel.  Problem is, I can't figure out how to ONLY cast a shadow.  I don't want the video in the shot, just the shadow.

 

Any help?

Headwax

welcome back Kodiak3d

:)

pretty sure you could try putting an avi of the inverted alpha channel in a spotlight gel

 

you could play with shadowcasting  shader mode as well but I don't think that would get you to the right place

 

have a read of this if you strike problems https://www.daz3d.com/forums/discussion/37158/spotlight-gel-question

Kodiak3d

Nice trick :-)  Thanks, Head Wax.  I'll have to play with it a little to get it exactly where I want it, but the effect works.  

I love learning new stuff about Carrara. :-)

Headwax

pleasure, Carrara is a deep well full of good things :)

DesertDude

This came to mind, probably not as elegant as head wax's method...but anyway:

From your compositing app, output your green screen footage as a black and white (and nicely edge feathered grey) mask

In Carrara, create a plane with the same dimensions/ratio as your footage. I made mine 640x480...or 6.40 ft x 4.80 ft in Carrara, then scaled appropriately

Create a shader for your footage, set all to 'none'. In the Alpha Chanel, drop in your footage, set to Alpha Only, then copy that into the Glow Chanel.

Whatever you are casting your shadow onto in Carrara, turn that shader into a Shadow Caster...I used a default Terrain.

In the Assembly room, turn your Background to pure white.

Adjust/Rotate your Light(s) to tatse and render.

I wish I had a final render, but I was in such a hurry I closed the scene instead of rendering and I am in a total hurry and can't make a new one at the moment but it works and you should have a shadow only on a white background.

Edit to say: maybe you don't need the Glow Chanel...will test later but I'm out the door. Bye for now