You may have heard this iMovie plug-in being referred to as the 'best-of-class compositing ('blue-', 'green-screening') plug-in'. But what does it do? Simply put, it allows you to intelligently blend a picture into a movie or vice versa. This is more than using simple transparency because it allows you to target a (freely definable) color in your picture or movie and make that color transparent. In TV, the color usually replaced by a picture usually is blue or green, hence the name 'green screening' (the actor stands in front of a blue screen). The best known (and probably most often) example for this technique is the weatherman in front of his weather chart. The process of intelligently combining two picture sources is also sometimes 'compositing'. The technique of replacing a key color with a whole picture is also called 'chroma keying'.