Filming on a green-screen is professionally known as Chroma Key Compositing, or Chroma Keying. The technique is primarily used to remove a background from the subject of a photo or video.
Keying is the process of isolating a single color or brightness value in an image and converting that value into a transparent layer allowing another image to show behind. Chroma Keying isolates a single colour, Luma Keying isolates a specific luminance value.
Chroma Keying works with any colour, however the most commonly used is green as it is the further colour from the colour of our skin.
To film on a green-screen you first need a green-screen in Chroma Green (#00B140). Green-screens can be either fabric or paper, you just need to ensure that they are free of creases and tears as these will reduce the ability to get a good key.
At Story Ninety-Four we use a portable integrated green-screen system that allows us to film a green-screen in any location.
The next stage is evenly lighting your green-screen as any variations in colour and luminance value will affect the key. You also need to prevent shadows on your green-screen so it is important to light your green screen and subject independently.
The final stage of filming on a green-screen is to prevent green spill. Spill is when the green reflections from the green-screen spill onto your subject creating a green halo. You can prevent spill by having your subject stand over 2 meters away from the green-screen or by flagging the spill.
Once you have finished filming, import your footage into your editing software and use the Chroma Key effect.