Chroma keying is a video image keying technique in which any motif, photo, text, graphic or video sequence is inserted as a background. In the realization, the object or person to be backgrounded is placed in front of a monochrome wall.
In chroma keying, the wall glows in a saturated blue or green. That's why it's called blue-keying or blue-screen, and if it's green, it's called green-keying or green-screen. The wall color is the color used for cropping the object and punching. To avoid chroma keying within the object to be cut out, the punch color must not be present in the object or person. After chroma keying, the cropped subject can be blended into another background, image source or scene, or even into a computer-generated background, Computer Generated Imagery( CGI).
Chroma keying is used in all film and video studios and is part of the recording technique. Examples include classic news broadcasts.
If the person to be recorded sits too close to the blue screen or if the screen is unfavorably illuminated, halo effects occur. These appear as blue or green halos on the head and shoulders of the person to be recorded.