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Chroma key

What is chroma key?

Chroma key is a visual effect in digital video that lets you replace a block of color (usually green or blue) with another image or video. Replacing the background in a video is the most common use for chroma key, and this is usually done by placing a large blue or green screen near the back of the shot. 

Why do we use chroma key?

The main use for chroma key is replacing the background in a video. Filmmakers use green screens and chroma keying to make it look like scenes are taking place in a fantastical or breathtaking environment — and not on a boring film set.

Chroma key isn’t only for feature-length films, however. Another common use is for local news stations doing weather reports; the reporter stands in front of a green screen and the weather map is added as a visual effect.

You can use chroma keying during the editing process, after you’re done filming. But you can also use it for live videos, like TV stations do for weather reports. If you want to use chroma key on your live stream video, you’ll need a green (or blue) screen and a chroma key software.

Is chroma key only used with green?

You don’t have to use green for chroma keying. Technically, you can use any color you like. Green is a common choice, however, because it doesn’t closely resemble natural hair or skin colors. With chroma keying, you have to remember that once you set a color to filter out, everything in the frame of that color will be filtered out. So if you choose light brown as your chroma key color and the person in front of the camera has light brown hair, their hair will be filtered out and become part of your virtual background.

For this reason, green is most often used. Blue screens are common though, too.

How to chroma key a green screen

To use chroma key, you’ll need a green or blue screen and a video software that allows chroma keying. If you’re doing it for a live stream video, you can use software like OBS Studio or Restream Studio.

To use chroma key with OBS Studio, follow these steps:

  1. Set up your live stream as you normally do — connect your cables, camera source, audio, etc.
  2. Add the visuals you want to key in as a new source in OBS. Place this source below your video source in the hierarchy. This tells OBS which are original and which are keyed-in visuals.
  3. Right-click on your video source, find it on the list of available effect filters, and click on it to apply it.
  4. You’ll see chroma keying applied right away, and you’ll also have some options for fine-tuning.

You can also use Restream Studio to chroma key:

  1. Go to Restream Studio and select the gear icon to open the Settings menu.
  2. Navigate to the Virtual Background section.
  3. Choose the key color (green, blue, magenta or custom) depending on your screen.
  4. Choose a virtual background.

As you prepare to use chroma key for your live stream, keep these tips in mind:

  • Remove anything from the set that’s the same color as your screen (and don’t wear something the same color as your screen).
  • Use a slightly bigger green screen than you think you’ll need.
  • Don’t let the person you’re filming stand directly in front of the green screen. It can create shadows.
  • Use enough lighting so the green screen is lit evenly. If there are shadows or bright spots, it will mess up your chroma keying.

For more tips on how to use chroma key, read our full guide to using green screens for live videos.