Green Screen with iMovie

Using a ‘green screen’, you can video a person and then superimpose them on top of another video or still image, by making the green background transparent. Green or blue backgrounds are used as they are the furthest colours from skin tones, making it easier to get a clean background removal.

Recent updates to iMovie for iOS and Mac now offer green-screen functionality, to instantly remove the background of clips shot in front of a green or blue screen.

Included is a 4-point mask for adjusting what areas are masked, and a strength slider to control the transparency. You can also import still images with transparent backgrounds for logos or custom graphics on top of your video.

Further Information
Here is a great demo video of using green screen on iOS and details of using the feature on Mac
To learn more about green screens, lighting and other tips, watch this video