What is this called?

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Ok so this is driving me mad, having a total brain fart. What is the name of the process where you take a video with lets say an actor in a room, you use video editing software to track the outline of the actor which then lets you remove the actor from the background.

Its not key framing, that;s a process using a green screen, this process is basically the opposite. I knew it but just can not remember, even tried looking it up on Google. Will know it if I hear it again.

UPDATE>>>>>

Nevermind, My brain fart cleared out and I finely remembered, It was Rotoscoping I was thinking of. Now I can start learning it.

 

[dugdiamond]

matte

 

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Just finely Remembered.... Rotoscoping. I kept thinking Rotopan.

This is the kind of thing I was looking for.

[media]http://www.youtube.com/watch?v=xYgfDUnA1Ys[/media]

 

[dugdiamond]

ahhh - that's what you meant

it is used in american football (and other sports) to superimpose graphics under the players, but on top of the pitch.

i know the chap who invented it, way back in the 80s. we worked together, programming, before he went to work in TV and film.

 

[Game Over]

Thats cool, I did not know it was rotoscope that they used in the Football games, Always wondered how they did that, cool as s***.

 

[dugdiamond]

the camera "mounts" must be a permanent fixture for it to work...

1. they take a panoramic sweep of the field of view, with an empty pitch..
   
2. then they XOR the view from the camera in realtime of the pitch "crowded".
   
3. the result is then subtracted from the video feed.
   
   (it looks like the "crowd" is playing on an alpha channel [in thin air])
   
4. they then take the panoramic sweep, then layer the graphics on top of that, and then finally add the alpha'd "crowd" on top of that one.
   

...

TIP: if you look very closely at a slow-motion HD picture of a football game that uses this... the players will be pixelated.... total give away, but as it happens at many frames/sec the human eye fills in the gaps.