what is Chroma key Compositing?

Chroma Key
Chroma key compositing is a special affecting technique for merge two videos or images together based on color. The technique has been used in many field to remove the background any picture or videos.  A color range in the top sheet is made clear, revealing another image behind. It can any be something you do after the camera work is done, or, with today video programming software, a way of modifying live stream video between the camera and the broadcast. Either way, it is a processing technique that produces the last picture.
The name comes from the technique, which involves filming the subject against a mono color background. Any color that is not found in the person himself can be used as the background, but naturally either a blue and green background is used. In compositing, the blue or green background is
 replaced by another image, which is called the “background plate”.

Chroma key Compositing used three things
1. Green color
2. Blue color
3. Magenta

Green Color
Green are used because it is considered to be the outermost away from skin tone. Green is currently used as a backdrop more than blue because image sensors in digital video cameras are most sensitive to green due to the more pixels to the green channel the human increased sensitivity to green light. The green camera channel contains the least noise and can produce the fresh key. Also less light is needed to green, again because of the higher sensitivity to green in picture sensors.

Blue Color
A blue screen will be used if the subject is predominately green
For example   plants Magenta Sometime a magenta background is used. Some software applications refer to it as "magic pink".The background color in the photography of the subject is normally green. However chroma blue is sometimes used if the subject is green. Any color can be used but green or blue color are common as they differ strongly from human flesh tones.The technique is most often used for painting, advertising and graphic art so that subjects are placed in location environments without needing to be on location. Chroma key techniques are widely used in professional photography to save location charges. It is also used in cinema, special effects work and act photography.

In T.v, chroma key techniques are used widely. An everyday example is weather forecasting. The subject stands in front of a chroma key backdrop screen. The background is digitally ignored by the software which isolates the subject from the chroma key color. In the transmission the two images are merge into a single image in the broadcast version. Modern TV technique is highly stylish. Subject and background can be combined and broadcast in one live transmission.Software for doing chroma key compositing in digital still photography is widely available. However, simple techniques in quality photo-editing software (such as Photoshop) can be used to create still chroma key composites without purchasing special software applications.
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