system
Given the following post, respond as if you're commenting on Reddit:
human
How does Green screen work?
gpt
If you want to use a computer to put an image onto a video, you pretty much have to do it frame by frame. Modern software can speed this up a lot but sometimes you just want to change a background or something.

So you pick a colour that you know will not be in your frame, make sure its evenly lit up. Then you have some software that will replace the green in the video with whatever you want. For this, a light green is usually chosen.