How to Use Chroma Key to Create a Visual Masterpiece

Have you ever wondered how filmmakers create those awe-inspiring scenes where actors appear to be walking on the moon, riding dragons, or battling in epic arenas?

The answer lies in a powerful technique called chroma key.

Often, video effects software allows you to replace a specific color in a video with another image or video, creating stunning and realistic special effects. This guide will explain how a chroma key works and walk you through the steps of using a chroma key and exploring your creative potential.

The best and most commonly understood example of a chroma key at work is when you watch the weather channel on television. The forecaster is standing in front of a map showing the landscape and incoming rain, snow, or even just an overlay of the current temperature. How did the weather channel accomplish this?

The simple answer is the presenter is standing in front of a chroma key, also known as a green screen. Production uses video effects software to replace the green screen with the map and upcoming weather forecast.

Importance of chroma key in videos and photos

Do you need to have a green screen for every single video or photoshoot? No, but you might want to have one depending on the style of motion picture or photos you’re shooting. Green screen is an important component to have when you’re trying to accomplish unique, creative, or stunning photos or videos.

Utilizing the chroma key effect for your visual projects can make the end results stand out and take your production to the next level. You can find the chroma key effect in video effects software. 

How does chroma key work?

The next time you’re watching your favorite movie and wonder how the actors got to those breathtaking locations or survived life-threatening situations, know that it’s not a specialized set but the work of a chroma key.

The actors stand before a flat green (or blue!) screen, act out the scene, and say their lines. Then, the production team uses video editing software and other tools to remove and replace parts of the footage. They make everything that is the color of the green background invisible and then replace it with footage of something else that will accomplish the desired video effect. The term used to replace the background with this footage is called keying.

You can edit anything into the background: actors exploring another planet, surfing in the Pacific Ocean, flying in a fighter jet, and, yes, something as basic as doing the weather forecast. 

When using the chroma key, it’s important to remember that to get it to work effectively, you have to replace the green screen background and cut out all of a specific color. There can’t be anything of that color in the actors or scenes you want to keep. If someone is wearing the same shade of green, they’ll be transparent, too. It’s best to keep green color out of the equation during costuming and wardrobe. 

A good example of a computer green screen gone wrong because of wardrobe occurred when FOX2 meteorologist Jessica Starr wore a green dress to show the weather forecast in Michigan. 

Source: Mirror

Thankfully, this was done intentionally to show the audience why weather forecasters should never buy anything green to wear because they’re always standing in front of a green backdrop at work.

Source: Mirror

Chroma key color codes

While most people know the chroma key as a green screen, you can also use blue to get the same effect.

The best shades are chroma key green and chroma key blue. They have unique color codes.

Not sure if green or blue is best? Green screens are great for daytime scenes, while blue screens are sometimes better for replicating night scenes. You also need to think of landscape and wardrobe. If the scene is in a forest with a lot of greenery and plants, choose blue. If your actors are dressed up like Spiderman, choose green.

How to create your own green screen

Unless you’re Ron Howard or Steven Spielberg filming the next Hollywood blockbuster, you probably have a limited budget for your project and likely don’t want to break the bank on green screen photography. Your two options are to make one yourself or buy an all-inclusive kit.

Make one at home

Unfortunately, making a chroma key at home is a little more complex than just painting a fluorescent green wall in your home. Here are some things to consider:

• Do you need the chroma key to be portable? Do you plan on creating your own studio space or need a background that can be moved and taken to a different location? Depending on the answers, you’ll want the fabric or material to be lightweight and stretchy.
• Do you have the time, energy, and patience to iron or remove wrinkles from the fabric? If you want to avoid this, use a heavier fabric that won’t wrinkle as easily.
• Will you film a scene with visual effects or just a close-up shot? A poster board could work for a short and sweet closeup shot but not for an entire green screen video.

Using a kit

If your budget allows, consider a pre-made green screen kit a fast and easy option to start your project. There is a wide variety available, ranging in price, size, and portability. Whether you’re only doing close-up shots or filming on the go, finding a kit that suits your needs is important.

Check out some options on Amazon or any other electronics retailer for kits that are geared toward beginners.

How to use chroma key

No matter what type of project you need a chroma key for, here are the best tips to help you start off on the right foot. 

• Choose a color: First, start with the right shade of green or blue and use a non-reflective screen material. 
• Separation: Keep your subject or actor at least six feet away from the screen when filming or shooting a photo. This helps avoid unwanted shadows on the green screen background.
• Get RAW: When it comes to the film being used, the highest bit rate or the least compressed codec is best. 10-bit color will always be better than 8-bit. While ProRes 444 and 442 are also good, RAW is the best option.
• Expose the background: It’s important to light your background and your scene separately. Proper lighting exposure for green backdrops helps avoid green light spilling or reflecting into the scene or shot. Remember, the green screen must be lit separately from the subject
• Eliminate motion blur: Filming with a faster shutter speed can help make the most of the colored backdrop for a crisper scene or shot. 
• Utilize a video editor: Video editing software with specific chroma key features makes replacing the green screen backdrop with the background image of your choice easy and hassle-free in post-production.

Chroma key examples in entertainment

There’s a really good chance that some of your favorite films use green screen effects during memorable action scenes. Check out some examples below of green screen scenes and how they come to life.

Avengers

It’s hard to talk about chroma key without mentioning the Avengers franchise, which features many green screen scenes. 

Below, you’ll see actors standing before a green screen, which will later be replaced and superimposed to show New York City under attack.

Source: Disney+

Another great example of the magic of the green screen can be found in Captain America: The First Avenger. Audiences see Steve Rogers hanging from a helicopter, attempting to land on top of a train on the side of a mountain in the middle of winter, when, in reality, the screen is entirely made of green materials.

Source: Disney+

Harry Potter

The Harry Potter franchise is another great example of many scenes being made possible thanks to the use of a green colored background. In the example below, director David Yates stands with actors Daniel Radcliffe and Emma Watson in front of a green screen.

After filming and in video production, the green screen will be replaced to show the two actors on top of a very high tower while the audience sees an expansive landscape below.

Source: WarnerBrothers

In reality, the actors aren’t atop a high tower at all but simply in front of a green screen.

Game of Thrones

Another must-mention is the Game of Thrones franchise. Every episode uses a chroma key and other special effects to create high-quality and visually stunning scenes. 

In the example below, the Knight King and his Army of the Dead stand in front of a green screen, which is then replaced with hundreds of other White Walkers standing in a blizzard at night. Video editors transform this green screen footage into a scene that wows audiences and provides shock value.

Source: Buzzfeed

Grey's Anatomy

Not every use of a green screen has to be totally out-of-this-world or futuristic. Instead, it can be as simple as two characters enjoying a glass of wine overlooking the city where the television show is set. 

For example, the scene below is from Grey’s Anatomy. It shows two actors winding down with a glass of wine overlooking the Seattle skyline. The scene has nothing supernatural, but a well-lit chroma key makes it possible.

Source: Digital Synopsis 

It may seem silly to use a green screen for the skyline instead of having the actors be in Seattle, but most television shows, including Grey's Anatomy, are shot in Los Angeles. 

Make other filmmakers green with envy

From action scenes to stunning landscapes, the chroma key turns an ordinary shot into something truly spectacular. With the right costume design team, lighting, and software, any scene or photo can go from ordinary to true art.

Now that you’ve mastered how to use chroma key, learn how to incorporate computer-generated imagery (CGI) into your next film.

This article was originally published in 2022. It has been updated with new information.