Having CG interact with a real environment

[ryan06]

I've seen many movies now where it appears as though CG is interacting with its actors and other earthly objects. Are these scenes all CG or was this done on a green/blue screen where the actor is on a layer in front of the action?

[Anhar Miah]

this question is way to open and wide ranging, what you could do is say, provide a specific shot/video, perhaps show us a video link or screen grab, then we can help to discuss it in more detail.

[Mattykins]

Well -

When you are dealing with a CG element being a character that actors must interact with you need to have markers where the element will be in the frame so as the actor can interact - and the compositor will be able to tell where the element goes.

Transformers did this by taking C-stands that extend to the height of the CG element and put a paper face on the top of the stand so the actors knew where the elements were.

Maybe that is close to the answer you were looking for?

[Martin Rivera]

ryan06, there several ways in which this can be done, but if you are asking about how to blend the CG elements with the live plates, then one method is to use compositing software, such as After Effects or Combustion, and to use masks (Rotoscoping) to BRING forward the person or object you want to appear in front of the CG.


If you are dealing with 3d Characters interacting directly with the actors, there are several methods for this also- one of which is modeling a 3d version of the actor and animating this model around the actor, and use that 3d model as a mask or matte object for the CG character.

There are various ways to do these things and it all depends your situation, budget, shot composition and camera movement and other things in that realm.

Hope that helped a little bit!