Virtual Backgrounds are fast becoming a common means of television and film production. A Virtual Background uses green screen chromakeying to create a set or stage that isn't real, and in some cases could not be. An actor or talent stands in front of or on a green or blue stage and a piece of hardware or software called a chromakeyer like an Ultimatte removes the color and replaces it with an image generated by a computer. This image is called a Virtual Background, which can be designed by an in house designer, a company that specializes in Virtual Background design or you can buy Virtual Backgrounds online. Virtual Backgrounds are ideal for situations where a real set is too expensive because of either space, location, or materials cost. Building a football stadium would be very expensive. Building a football stadium made of gold on the moon would be impossible, but not with a Virtual Background. A small stage covered with a green screen or blue screen and adequate lighting is all that's needed to put your talent anywhere your imagination wants to put them.

Getting a good even color behind the talent is the first step in chromakeying, this usually requires a chromakey backdrop in the form of cloth or paint. Chromakey paint can be picked up at hardware stores or lighting places like Studio Depot (Burbank, Ca), green cloth can also be found many places. Some companies sell blue or green pop up chromakey backdrops which travel easily and popup like a windshield shade.
Another alternative is Chromatte, a unique retroreflective material which is gray to the eye, requires little or no light, and casts no spill on the talent because the material is gray to the naked eye. But to the camera it sees it as a perfect blue or green. This is because of the Litering, a ring of LEDs around the lens which casts blue or green light onto the Chromatte material. Chromatte is also very portable in the form of a Chromaflex, a 7x7 popup which folds down into a 3 foot hoop.  

Sometimes Chromakeying is referred to as an art, because getting a seamless composite is less like a science and more like cooking; you need the right tools, the right ingredients, some imagination, and a lot of elbow grease. Traditionally the best way to chroma key is to light the background and the subject separately, this means that the backdrop gets a relatively even coverage of lighting, usually fluorescent, because most chromakeyers are susceptible to lighting variations and will give an uneven key. The talent is then lit to try and simulate the lighting environment of the Virtual Background. This can be difficult if the set is dim because of the immense amount of light usually required to get an even key on the background and further exacerbated by the fact that the more light you put on the background, the more spill you get onto the talent's head and shoulders. An Ultimatte will fix up the spill, but not all keyers have this feature so special care must be taken when doing traditional chroma key lighting for Virtual Backgrounds.