Video Keying - Chroma Keys

Continuing in our series about video switchers, I wanted to speak on a topic that is seldom completely understood but is powerful and a fundamental feature. Let’s talk about Keying!

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Keying is the act of placing one video source layered over another.  When most people think of keying, the example that comes to mind is usually a weather channel chroma key. What they might not know is that there are several different types of Keys. The types of Keys we are going to cover are Chrominance Keys, Luminance Keys, Linear Keys, Pattern Keys, and DVE Keys. Each type of key has a different use and can help your production in different ways.
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The first Key we are going to cover is a Chrominance Key or more commonly known as a chroma key. The most common place to see one of these is the weather segment of the news. Color replacement is the basic theory behind this key. To set up a chroma key you must place a person or object in front of a solid color, such as the commonly used bright green or blue backgrounds. We then can use the controls of the switcher to select the color we want the switcher to replace with a secondary image. 

Typically, a video switcher will possess a number of options for you to adjust including hue, gain, Y suppress, and others. The important piece of information to remember here is that a switcher will only pick one color and a small range around that color for recognition. So, lighting is particularly important to keep the color consistent for your switcher to see.  ​

Chroma keys are not just for weather reports but to set up interesting interview backgrounds for podcasts and other online events. If you set up a different chroma key, say one for each of your three cameras, you can create the illusion that you are cutting around a virtual set. 

Another use for this type of Key might be for putting lyrics on a stream. If you connect a graphics source, such as Propresenter, and put white text over a green colored background you can have the switcher remove the green color and layer the text over your video. Another great thing about using a chroma key is that it allows you to keep a thin outline, such as a black line around white text, for easy readability. If you need help setting up a chroma key or ideas on how to better use one for your production or stream, reach out and drop us a line!