The Green Screen Explained

I have seen on several online forums confusion about the legendary “green screen” and the magic behind it.

First, a lot of people tend to think there is some magical properties behind the green screen.  I have even seen people walk into a studio just to see “the green screen.”  News flash, people – it’s literally a green piece of fabric or a painted wall.  The technical name for this is a chroma key screen.  Mostly green or blue screens are used for this process of chroma keying.

The reason that particular shade of blue and green are used is because there is not any of that color in the pigment of the human skin.  Green is used more often, largely because blue is a popular color in clothing and it is much easier to avoid green clothes when going in front of the camera.  That’s it.  You could literally use any color background for the same process, it would just depend on what you’re shooting as far as how it would “key out.”  If your screen and your subject are too similar in color, it will not look as good and your subject might look like they are missing parts, as seen in the picture below.

So you might still be confused as to WHAT exactly is the purpose of the chroma key screen.  How does it work? What does it do?  Let me break it down for you as simply as I can.

“Chroma” = color.

“Keying” is a term we use in the video editing world which means, “To remove.”

Remove the color, or ‘key out’ the green, and you are left with nothing more than a transparent background.  Then, you can take anything (photos, video, etc) and put it behind your subject where the green screen used to be, and voila…chroma key magic.

Imagine if you have construction paper, and you draw a person on the paper.  Your person is bound to that background. It is very hard to manipulate the background without affecting the drawing of the person.  Now, what if you cut out the person from the construction paper and then placed it on any background you wanted? This makes things a lot easier.  That is the same as chroma keying.

The most common place you see it used is on your local news station.  Meteorologists use a chroma key screen to show the audience their weather graphics.  They have monitors in front of them and off to the sides where the audience can’t see and these show the same thing we see at home, them with their weather graphics.  This way they can see at what they are pointing.

In television, a computer looks at the image and anything that is that shade of green it replaces with the graphics from another computer with all the weather info and graphics.

So you see, the magic isn’t in the green screen itself – the magic is in the software that removes the green screen.

Once you have keyed out the background, you can continue to manipulate the image in amazing ways.  You can move your subject anywhere you want, you can put any background in its place, the possibilities are almost endless.

This process has become a staple in Hollywood, as nearly every movie you watch nowadays uses this technique somewhere in the film.

Whether it be to extend or alter a set, make someone appear to fly, or literally hundreds of other purposes, chroma keying is one of the greatest inventions in the world of video and isn’t going away anytime soon.


2 Responses to “The Green Screen Explained

  • Great information! Exactly what I was looking for! Thank you!

  • Excellent! This website gives helpful information to us, keep
    it up.

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