What is Chroma Key?

What is Chroma Key

We hate to spoil the surprise, but the truth is that famous actors aren’t actually scaling a skyscraper, jumping off of a waterfall, or coming face-to-face with dinosaurs.

We know. It was a big blow to us, too.

Instead, filmmakers of all kinds use chroma key to take their video clips, advertisements, and even weather reports to the next level by changing the background of a shot.

Chroma Key: The Basics

You’ve probably heard of actors standing in front of a green or blue screen during the filming process. The green screen behind them is later replaced with background images of skyscrapers, natural disasters, space, battle images...pretty much anything a director can dream up.

But what actually transforms that solid-coloured screen into the impressive background landscapes and action shots we see in movies? And how can you take your video content to the next level without having to fly your whole team to a remote island?

Chroma key.

During the chroma keying process, the chroma (the green or blue screen) is taken out of the shot and then replaced with the desired background. Only the green or blue colour is removed from a specific section of the shot -- so that the weatherperson, actor, or guy at home filming a video for his YouTube channel isn’t turned into a blue or green alien.

Once the green or blue screen has been digitally removed, you can add in pretty much anything you want in addition to your original image -- whether it’s an object or an entire background.

So, instead of holding dragons or weapons, your favourite actors are actually holding weirdly-shaped green objects. Check out these pictures of the Game of Thrones dragons in production -- we think you’ll agree they’re a lot less threatening than the real thing.

Consider it just one more piece of movie magic.

Why Blue or Green?

So, what made green and blue the staple colours of the chroma key process?

Funnily enough, it all started because weathermen usually wear blue suits when giving the report. A green background provides enough contrast with their suit colours, so a map of the region can easily be projected behind them.

Green also isn’t exactly a natural skin tone. This means that the hands, face, and any other body parts of actors and actresses won’t disappear into the green screen. Green and blue provide the highest amount of contrast with all skin tones.

We know what you’re thinking: what if the actor is wearing a green or blue dress -- or the objects and backgrounds to be added in later are blue or green?

Most importantly, it provides the opportunity for amazing things like this to happen.

But on the set, another colour would simply be used for a background screen.

What Makes the Chroma Key Process a Success?

The success of the chroma key process depends mainly on one thing: lighting.

The background screen needs to be evenly lit so there’s no discrepancy in colour and shadows are kept to a minimum.

Usually, those shooting will work with two different sets of lights.

This will prevent shadows and ensure there’s a sense of distance between the subject and the colour background. Depending on what someone is shooting, they may even invest in some matte sprays to stop light reflection from changing the colour of the shot.   

Chroma Key: The Secret to Video Success

OK, so maybe you’re not likely to be called up to shoot and direct Hollywood’s next big blockbuster.

But that doesn’t mean that you can’t benefit from a basic understanding of the chroma key process.

Use this knowledge to shoot successful marketing videos without blowing your budget, or create compelling video content for your website and social media pages.

Of course, you can also use chroma key to convince your friends you’ve gone on the vacation of a lifetime, met your celebrity crush, or moved into a mansion…