Chroma key

Chroma key is like magic for TV shows and movies. You know how sometimes the weatherman shows us the weather even though they are not at the beach or in the rain? They are actually standing in front of a big green screen. The big green screen is called a "chroma key."

The weatherman sees what's behind the screen on a special TV monitor. The camera that's filming the weatherman doesn't show the big green screen behind him; instead, the camera just captures his image. Once the weatherman is filmed, the TV editors use a computer program to take out all the green in the image and replace it with whatever they want - like an ocean or a cloudy sky.

This magic can also be used to make special effects in movies. For example, if a movie needs a scene with a giant dragon breathing fire, the actors won't be able to see it on set because it's not really there. Instead, they act out their part in front of a big green or blue screen, and later the dragon and the fire are added in with special computer tricks. It's like having an imaginary friend who can do anything you want - but on TV and in movies!