Video Keying

Luminance and Pattern Keys

Keying is a powerful and essential feature on your video switchers. It's important to know the basics behind keying so you can really understand what is happening on your switcher when you use these features. We've talked about Chroma Keys, HERE, so now we want to highlight another similar switcher key: Luminance Keys.
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Luminance keys another great keying tool are remarkably similar in relation to chroma keys, but instead of removing a color they remove and replacing it, this key is based on luminance. Also known as white vs black. With this key, pure white stays white and pure black is replaced by video. Everything in-between is transparent.  
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For example, if your main source is a camera and you wanted to add a GFX source that was white text with a black background, you could use that as your source and fill. The switcher would do the rest by removing the black and leaving white lyrics over your video. This is a great way of quickly adding lyrics to your stream feed without any special hardware. If you use ProPresenter you can either add a second output without a colored background or you can even use your stage display feed. We call this our cheat key. Up until the last year, it was a common way of building keys for lower budget video setups to getting lyrics onto a stream.  
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The negative of using a Luminance key with a single graphic source is darker shades. Let me explain. If you use black, such as a black letter border, or any black in the graphic design, then that black will also become transparent. It’s not possible in a single source key to have white lyrics with a black outline. This could make the lyrics disappear against your video at times making it hard to read.
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If you need to be able to do more than white over black, another option that many switchers will provide as an alternative to using the Luminance key is the Pattern key. A pattern key allows you to take a single input source and cut it by using a preset pattern to overlay that source over another. The easiest way to think of this is like a pattern wipe transition. You adjust the space you want to overlay using cropping controls in the switcher until it cuts out what you don’t want and shows what you do want. A great way to use this is with a true rectangular lower third graphic. A pattern key can cut that lower third area and replace it with GFX over a camera feed very easily.
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