Limelight
What is Chroma Key?
Chroma key is a video compositing method that makes a chosen color transparent so a different background can be layered behind the subject.
Chroma key works by selecting a single, evenly lit color in a frame and treating every matching pixel as transparent. The software then composites the remaining subject over a separate background image or video. The technique is named for the chrominance (color) channel it keys against, and it is the foundation of weather forecasts, virtual studios, and many streaming overlays.
Chroma key is often confused with luma key, which keys on brightness rather than color, and with rotoscoping or AI background removal, which trace or infer a subject's outline without needing a solid backdrop. Chroma key needs a controlled colored surface; the newer alternatives do not, but they trade accuracy for convenience.
In presenting, streaming, and recording, chroma key lets a host appear over slides, gameplay, or a desktop. It is a property of the camera and the compositor (OBS, video editors, conferencing apps), not of on-screen highlighting tools. Limelight is a separate layer: it draws cursor spotlights, keystrokes, and annotations directly on your live screen, and does not record, composite, or remove any background.
Why Limelight
- ▸Keys out a specific color, classically green or blue, that does not appear in skin tones
- ▸Requires even lighting and a wrinkle-free backdrop for a clean edge
- ▸Implemented in compositors like OBS Studio and in most video editors
- ▸Distinct from luma keying, which keys on brightness instead of hue
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FAQ
- Why is green used most often for chroma key?
- Green is the farthest common backdrop color from human skin tones and is bright on digital sensors, which makes the key edge cleaner. Blue is used when a subject wears green.
- Does Limelight do chroma key?
- No. Limelight is a macOS menu-bar overlay for highlighting your cursor, keystrokes, and annotations. It does not composite video or remove backgrounds.