Colour keying is a technique that creates transparency from footage with subjects shot in front of a prepared green backdrop. Colour keying is a common compositing and special effects technique and is relatively easy to achieve with the right planning and footage capture.
In After Effects there are a number of plugins we can use for keying, but Keylight is usually the best option. Keylight was developed for feature film production but now ships as part of After Effects.
With Keylight, we basically choose a colour in our footage to generate a track matte from. We can then refine the track matte depending on the quality of the lighting and camera work of the footage.
This demonstration utalises the following stock footage:
