fading in a charcater…

[Steve Roberts]

You may think this would be simple, but it’s not. The computer doesn’t know what is talent and what is background, so you have to tell it. All it knows are RGB values, so you have to say “these RGB values (colours) are talent, and these are background”. That’s called keying. Normally, the footage is shot in front of a uniformly blue or green background, so you can tell the computer that the blue pixels are background, and everything else is foreground.

However, if your footage was not shot that way, pixels in the foreground will match the colours of pixels in the background, so you won’t be able to key out (remove) one or the other without seeing a lot of holes. You’d have to manually draw masks around your talent, and animate the mask shapes. This is called rotoscoping, and when motion graphic artists go to Hades, that’s the job they’re given down there. Look in the AE help for mask information, and search the COW for “rotoscoping” if you like.

Some may recommend the “difference matte” effect, where you compare an image of the background with the foreground, but in most scenes, I’ve found that it doesn’t work very well when colours in the background “difference layer” match colours in the foreground.

You may have to start drawing masks.

[Ryan Hill]

Is anything in the background moving?
Do you shoot the footage hand-held or on a tripod?

A still background and tripod would make this much easier.

[Karim Daire]

In case the footage is shot still from a tripod you could mask out the left/right where the character comes in and goes out. Generate a still of the background without the character and put in the garbagedmaked character with a soft feather on the mask edges. Add a dissolve on the beginning an end of the layer or where the character comes in/goes off. If nothing shakes and light doesn’t change this could work well without tedious rotoscoping.

Karim