Chroma key (commonly called green screen) is a post-production technique that replaces a solid-colour background in filmed footage with a different image or video.
Why it matters#
Chroma key gives a production team control over the presenter’s visual environment without requiring a physical set. The presenter is filmed in front of a green (or blue) screen, and the background is replaced in editing with any image, graphic, or video. This is useful when a physical location is unavailable, inconsistent, or unsuitable for the content.
How it works#
The camera captures the presenter against a uniformly lit, solid-colour backdrop — typically bright green, because it is furthest from natural skin tones. Editing software identifies all pixels matching that colour and makes them transparent, allowing a background layer to show through. The result, when executed well, looks like the presenter is standing in the replacement environment.
The quality of the result depends almost entirely on lighting. Uneven light on the screen creates colour variation that the software cannot cleanly remove. Spill — green light reflecting onto the presenter — creates a colour fringe around the edges that is difficult to eliminate. Both problems are solved at the filming stage, not in post-production.
Key facts#
- Lighting the screen evenly is the technical priority. Two lights positioned at 45-degree angles to the screen, equidistant from it, produce the flattest, most consistent colour.
- The presenter must not wear the key colour. Green clothing or accessories will become transparent in post. Blue screen is the alternative when the presenter must wear green.
- Chroma key is a production decision, not an editing one. The screen must be set up correctly on filming day. Poor footage cannot be rescued by more sophisticated software.
- Distance between presenter and screen reduces spill. The further the presenter stands from the screen, the less green light reflects onto them.