Chroma Key comes under many names including Chroma Keying, Colour Keying, Matting, and Colour Selection Overlay; however, it is most widely recognised through blue or green-screens on television.
The simplest way to understand Chroma Key is to think of the nightly news. Contrary to childhood beliefs, the weatherman is not actually standing in front of giant map with little rain clouds floating about, he is actually standing in front of a blue or green screen. This background key colour is digitally removed or becomes ‘transparent’, and replaced with the foreground from another source, in this case the image of a weather map.
The reason blue and green are used for the background screen is because they are least like human skin, therefore a clear distinction can be made between actor and screen. It is crucial elements such as whether the actor is wearing blue or green that must be taken into account when using a colour screen. Colour conflicts will not end well when viewers are watching explainer videos or the nightly newsreader.
The key to obtaining quality Chroma Keying is not in available software, rather in the lighting used. Always use a background screen with a high intensity indirect light. This, coupled with low-light focus on the subject or actor, will result in a suitable contrast between light levels and allow a greater affect. To capture the perfect image on screen, it may be necessary to move lighting around, also consider using elements such as screens, umbrellas, and white walls until your desired lighting is reached.
Despite its worldwide usage, Chroma Keying requires meticulous attention from skilled individuals. Issues such as camera movement, positioning and lighting can drastically alter the final image displayed on viewer’s televisions. Lack of attention to the Chroma Key has resulted in ‘fringing’ (sparkling and jittering on actors outline) in the past. However, these days, camera movements are digitally controlled and therefore there is less chance for camera movement and magnification of unwanted distortions. Still, it is best to exercise caution when using Chroma Keying for your explainer videos.
The Chroma Key technique is also prevalent in the entertainment industry where special effects are widely used. Notable examples of where Colour Keying has been used include Star Trek and Star Wars. Thanks to Larry Butler, who first invented Colour Keying for his films in 1940, countless actors have been saved from difficult situations such as being put in space, under the sea, or in flying cars.
Special effects have certainly come a long way since the 1940’s when colour screens were first used, however, we are still reaping the benefits of Colour Keying today, and it looks unlikely to be replaced any time soon.