View Full Version : Compositing

04-04-2011, 02:54 PM
Hey guys (and gals),

So I was working on a scene where an actor makes some daggers out of ice and flings them at someone. How I'm doing it is: I've got a particle emitter, that makes the ice type stuff, and objects in the shape of daggers. I am aware of the basics of compositing-
that's an image I made all on lightwave a while back...
So, how do you make a scene where the CG aspects go in front AND behind the actor? like, say, the last airbender?

04-04-2011, 04:12 PM
You have to create a series of masks that outline the actor. This process is often called rotoscoping.

I understand that the new Adobe After Effects that is part of the CS5 Video Production suite has some great new tools built in for this type of thing and make it considerably easier to do and automate. There was a clip about this over at fxguidetv, I beleive it was episode 81 but I can't be sure as out IT department is running IE7 and their flash page doesn't run correctly. (HTML OPTION PEOPLE!)

04-04-2011, 04:22 PM
Ok, then what do you do in LW?

04-04-2011, 04:55 PM
Basically render out your elements in LW with an alpha, then bring that into your comping program for the magic.

What Dexter was referring to is the new Rotobrush in AE. It works by trying to separate moving foreground element(s) like an actor, from a background that presumably doesn't move very much if at all. It actually does a pretty good job, but you do have to watch it and make adjustments as necessary. This Rotobrush effect could then be used as an additional alpha channel for your LW elements where needed.

04-04-2011, 05:05 PM
cool! we live in the same place!
but how do you make things go behind the actor and in front in the same clip?

04-04-2011, 06:36 PM
If you roto out your character you could map the video to a poly and then have your emitters animate around them.

04-04-2011, 06:43 PM
How did they do it with "the last airbender?", I'm trying to do something similar

04-04-2011, 06:44 PM
You plan ahead.
You think in layers, like Photoshop.
If you know you want something behind the actor but in front of the background, then you will probably want to shoot a clean image of the background this is called a "plate".
Then you would want to try to capture the actor against a backdrop that will key out as clean as possible.
Create the rotoscoped matt sequence of the actor.
Create your CG elements with ALPHA.
Begin to stack the elements together with your compositor.
CG element you want "behind" the actor.
CG actor element
CG element desired for foreground

That is really over simplifying things. But it is the general idea.
Plan ahead.
Make the pieces you need.
Put the pieces together.