Chroma keying or how to make people run through scenes of dinosaurs

In an example of a common application of chroma keying, a weather person walks around and points in difference directions in front of a blue background. A camera pointed at the weather person scans along with a computer that generates the image of a weather map. As television sets scan along with both the video and the image, viewers see the weather person at each point on their screens where the weather person actually is and see the weather map wherever the weather person is not. If the weather person makes the mistake of wearing a blue shirt, chroma keying provides a grisly peek at the weather map through the weather person's chest. You can learn more about this at http://www.seanet.com/Users/bradford/blu... Movies like "Wag the Dog" actually talk about this process of filming a star and props in front of a blue screen acting as if something very dramatic was taking place even though all you see if the actor and the blue screen. Then using hardware and software, the blue screen is replaced with either another image or other video. In "Wag the Dog", the star was carrying a bag of chips and running frantically. When the replacements were done, the blue screen was replaced with scenes from a war zone and the bag of chips was replaced with a small pet. Many many movies today use this technique or related techniques. You can read more about how movies use this technique at http://www.howstuffworks.com/blue-screen...

If you take suitable video of a person or persons or other objects in front of a blue screen which has adequate uniform lighting and if you then arrange for the video to be digitized on your hard drive, you too can perform chroma keying to key out the blue and substitute for it images or video of your choosing. Adobe Premiere, http://www.adobe.com, is a software tool that not only allows you to perform editing of your video by selecting portions of the video and either deleting these portions or moving them into other places. It also allows you to remove a blue background and substitute in another. Your ability to remove the background well will depend on how accurately Adobe Premiere can identify the blue. To be completely honest here, you could remove any one color, but blue is most commonly used with perhaps green a second choice. The Adobe Premiere software retails for around $600 or around $300 academic pricing.

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