hi. what would be the best technique for taking certain characters or subjects out of an existing video context and inserting them into a different footage, if those characters and subjects had not been originally shot against a blue/green screen? in other words, how to key out the unnecessary background in the original video, if it doesn't consist of just one colour? thanks.

You could rotoscope (mask) out the characters and then blur the mask a bit to round off the edges, or perhaps apply a choker to eliminate some jagginess. It will take a long time, especially if there is a lot to do and there is movement in the scene.

Hope you have a lot of patience!

(Of course, there are probably other, better ways, but rotoscoping would be my first bet. Good luck!)

~Loggie B

at last, someone replied! bless you.
you mean rotoscoping frame by frame like i'd do that in photoshop, for example?

Yup. Rotoscope (drawing a mask frame-by-frame) is usually the best way to handle this.
AE has a rotomask tool that can help a bit, since it is a vector shape that is keyframe animated. This means you don't have to animate every shape for every frame.

Check out Scott Squires Rotoscoping episodes from his Effects Corner podcast for some more background and tips:
http://effectscorner.blogspot.com/2006/01/rotoscoping-part-1.html

rotoscoping wouldn't be frame by frame- depending on the clip ..
with AE/combustion you rotoscope frame 1 .. maybe jump to frame 16 .. then
see how AE/combustion auto adjust the matte for frames 2-15 - if off then maybe you go and fine tune frame 1,8,16 - then see how AE handles 2-6 and 9-15 .. if off you then maybe go and adjust 1/4/8/12/16 which will probably get it right - all depends on how much motion is in the shoot ... if you rotoscope everyframe manually you usually end up with chatter on the edges of matte ...

thanks a lot.
sounds like i need to urgently get a copy of AE.
have only got FCE and AP. any chance of achieving the same results with those apps?

Try a difference key before you rotoscope. If the difference key doesn't work, use rotoscoping to clean it up.

2- Unfortunately, difference keys don't work too well when the b/g is moving. And you need a clean b/g plate (that's not too hard to make though if you photoshop it together from different frames).

Try a difference key before you rotoscope. If the difference key doesn't work, use rotoscoping to clean it up.

2- Unfortunately, difference keys don't work too well when the b/g is moving. And you need a clean b/g plate (that's not too hard to make though if you photoshop it together from different frames).


Yep! If the camera is locked off (not moving) and the background is also static, then a difference key will pick a moving subject out with some level of success.