View Full Version : replacing an arm with a CGI weapon

06-04-2011, 08:23 AM
sorry if this is the wrong forum i wasnt sure where to put it.

I was wondering if it were possible to replace an actor's arm with a cgi gun or sword? (Similar to Evil Dead or Grindhouse) I was looking into programs like Maya and Cinema 4D.

Anyone have any tips?

06-04-2011, 09:47 AM
Yup. My experience was with LightWave, as director, not CGI. The tools to accomplish this are advancing daily, so my advice may be out of date. In particular, tracking itself has improved.

Create for the actor a thin rod that will form the base of the CGI weapon. Attach this securely to their arm, velcro, whatever. A big part of selling this is the acting. Remember to tell your actors what the final thing looks like, size, weight, kickback, etc.

The small rod should be painted a different color than what the actor's wearing, or try the ping pong ball thing. The CPU will use this as the basis for rotoscoping in the CGI, camera tracking, etc. It doesn't have to be big - just give the computer enough tracking/movement data to avoid headaches later.

Some things you will want to consider:

1. It might help the computer if you could mark off some + signs in tape in the background scenery. If that's greenscreen, definitely tape. It it's run and gun, hopefully your scene has enough detail to track. This part helps match the CGI effect with the background plate.

2. Take some photos of the scene in which the action takes place during shooting. Sky, backgrounds, a full 360 if possible. This will serve as the CGI reflection map, and help make the lighting match the shot video and CGI.

If you do at least those 2 things, given properly lit and exposed video, then almost any capable 3D artist should be able to turn in something passable.

Others can surely chime in with their more informed advice.

Good luck.

06-04-2011, 10:37 AM
Watch the special features on the Planet Terror DVD for more ideas! RR always has awesome special features on his dvds.

06-04-2011, 03:48 PM
haha i actually watched it and saw what he did. I just have no idea what program I should use. He did it all in post