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 Chroma Key

Sometimes Chroma Keying 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 Chroma Keyers are susceptible to lighting variations and will give an uneven key. The talent is then lit to try and simulate the lighting environment of virtual sets. 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 sets.

 Chroma Key Backdrops

Getting a good even color behind the talent is the first step in Chroma Keying, this usually requires a Chroma Key backdrop in the form of cloth or paint. Chroma Key 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 Chroma Key backdrops which travel easily and popup like a windshield shade.
Another alternative Chroma Key backdrop 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 which is great for Chroma Keying. This is because of the Litering, a ring of LEDs around the lens which casts blue or green light onto the Chromatte. Chromatte is also very portable in the form of a Chromaflex, a 7x7 popup which folds down into a 3 foot hoop idea for on location Chroma Keys.






     
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