View Full Version : Interaction with live footage

12-06-2009, 07:29 PM
How can I make 3D characters interact with live footage and people?

Some examples are,

A creature bursting open a double door.

A Octopus snatching someone with their tentacles and dragging them away.

A creature tipping over a chair.

Does anyone know how, or know of any tutorials on how to do this?


12-07-2009, 06:23 AM
u mean with live broadcast footage? if thats the case I would assume u would need to make allot of diff animations for every situation. At the stadium I work at we have a mascot simply throwing a pie in someones face but the character isnt right there or appears to be right there next to them. just an overlay with alpha. I would assume u have to have some of the shots fixed to get scale and composition just right.

12-07-2009, 08:46 AM
If you mean live as in filmed and not as in "happening now" one of many possible ways would be:

First film the background without the chair/element/person that the 3D object will affect.

Then decide it it will be more work to recreate the chair/element/person in 3D. If not, you can film them moving around with string or something like that.

Then, if you still use a live element, use your compositing program to generate a difference key against the background that you shot in step 1. That will give you an alpha of that element.

Load the footage that has your moving element into LW as a background sequence and animate your 3D tentacle to match. Do't worry about the parts where the live chair would cover the 3D object for now. Then, render the tentacle with alpha (no background).

Then go back to your compositing application and set the background, the difference keyed element and the 3 object with it's alpha.

Finally, manually adjust the masks where the tentacle goes in front of the chair.

12-07-2009, 12:05 PM
It's about a billion times easier if the live action is shot with a locked down (non-moving) camera, too. Otherwise, you need some sort of tracking software so your LW camera makes the same moves as the camera that shot the scene.

12-08-2009, 07:59 PM
Look for making of featurettes and documentaries for movies that have this kind of interaction. I've seen some good behind-the-scenes footage from "Who Framed Roger Rabbit?" and there may be some good stuff in some kids movies like the "Stuart Little" and "Garfield" movies (I'm not sure about the last two).

12-09-2009, 05:05 PM
A Octopus snatching someone with their tentacles and dragging them away.

A creature tipping over a chair.

For the first one you need two people with markers which interact and in comp they keyed out later (rotoscoping). For second - film an empty chair and make the seat as collision object - but the snag is to get the original Set Lightning (HDRI), Rendering passes and Composting seamless together.

Making of District 9 (.MOV)

Making of Snickers

Final Clip:

Post your results here :)

12-09-2009, 07:19 PM
For busting open a door or tipping over a chair I would look at investing in a green screen suit if you don't want to roto.