What is Keying?
Keying is the process of singling out a single colour or brightness value in an image and using a piece of software to make that value transparent, allowing another image to show through the affected areas as in the background you want to add to make it look like your in a different country. Luminance keying, or lumakeying, is the process of keying out a brightness value or range, like black or white. Luminance keys are often used for applying mattes. Colour keying, or Chroma keying, identifies a specific colour to remove.
What is a Green Screen?
A green screen is a piece of material that is put behind a person or object hanging up and/or on the floor where you can then record and place it into a piece of software to then change the green screen (background) to anything of your choosing.
Many people use the terms Chroma keying and green screening identically, but the principle that powers chrominance keying is not limited to green. In the visual effects world of places such as Hollywood, blue screens are far more common than green. The main reason green is used is because of the contrast. In order to single out one area from the rest, the background colour must be very different. Bright green usually beats a blue screen mostly because it is not a colour commonly found on many animals or people. Any clothing that does match the background too much will key out, making a hole in the subject’s body, or making them invisible altogether.
It is also quite simple to make your own green screen too! Making sure you have a green background, a good balanced source of light and a tripod or a way of keeping a camera completely still and focused.
Not my image: Google.com