Used to be there was the subject, the camera, and the subject appearing on-camera, like this:

Then we got rid of the camera, replaced it with motion capture, and got this:

And finally we added the camera back in and combined it with motion capture to achieve this:

Once Andy Serkis played Gollum and Zoe Saldana played a blue alien, it didn't take people long to figure out actors could play other humans, too, and avoid anachronistic makeup or prosthetic sessions. The most interesting manifestation of this is in the new Tron movie, where Jeff Bridges will play the same character (Clu) he played in the 25-year-old original. The twist is that modern-day Jeff Bridges' actions will be digitized into younger Jeff Bridges on-screen!

"Now you can play yourself at different ages, whether it's a younger version of yourself or an older version of yourself, digitally," said Bridges in this Times piece explaining the concept.

This is kind of mind-blowing if you think about it. With this technology, inter-quels (i.e. movies between sequels) become possible: Bruce Willis could go back and do Die Hard 1.5 with his 1989 physique and hair, for instance.

It's also disturbingly possible that Hollywood could use archival footage to digitize, say, Cary Grant's face, body and voice, and have George Clooney play Cary Grant playing a movie character. Which is to say, George Clooney in the studio does a take, and the audience sees and hears Cary Grant doing the same take on-screen. Thus you could have long-dead film stars more or less "starring" in completely new movies.

What ramifications might this have for the rest of us outside the film industry? One application I can think of, as the technology trickles down and becomes affordable, is video chat. There's been some debate as to whether or not people will want to "put their face on" for video chatting, but with self-modeled avatars that are always clean-shaven, or wearing makeup, or dressed nicely, perhaps it will become more palatable. It's like a high-tech version of those tuxedo-print T-shirts.

While that's harmless enough, I do hope they leave dead stars alone. Hollywood already tastelessly "resurrected" Humphrey Bogart, Louis Armstrong and Jimmy Cagney for a Diet Coke commercial back in 1991. If digitization and motion capture makes these deceased stars capable of feature-length projects, it will only serve to reinforce the notion that celebrities are immortal. And that's ridiculous, because they aren't.

Only Tron is.