What is chroma key? It is a technique for mixing two images or frames together in which a color (or a small color range) from one image is removed (or made transparent), revealing another image behind it. Still, a visual technique is better explained in visual terms, so watch this video, which explains it much better than I ever could. The technique is also called color keying, colour separation overlay, greenscreen and bluescreen.

[via Holger on FB]