Chroma Key using the green screen can be one of the most effective tools a home digital video producer has for using locations and special effects that they may not normally have access to. With this you can isolate people and transform them to anywhere in the universe, as long as you know what you are doing. A green screen is a sensitive tool and will only work the way you intend if you follow certain principles.
The first thing to remember when using a green screen is to make sure that it is fully and equally lit on every area. You also need to make sure you are an adequate distance, usually ten to fifteen feet, away from the screen to cut down on reflection. Once you have these things covered you can begin to really utilize the versatility of the apparatus.
One of the really fun things you can do with a green screen is use it to transport your subject to a different location. To make this look realistic you have to make sure that you know what the location will be and make them act accordingly. For example, if you are going to have them walking in the desert they are going to have to alter their normal movements to be conducive to the elements of the landscape. Try looking at the picture or video clip ahead of time and block their movements accordingly. If you are going to want them to interact with movements in the background you have to make sure you know where and at what speed those movements will take place.
Once you decide on a background you can easily make parts of their body transparent in post-production. To do this you simply put a color of green on them that exactly matches the shade of the green screen. Green screens tend to be a very bright shade of Kelly green that is difficult to find, so this may take some searching. Decide on what parts of their body you would like to disappear and then use items that will focus in on this. These may be things likely appropriately colored clothing or a mask covered in green paint.
No matter what your purpose is you have to plan it well before jumping into the studio. Green screen is difficult to shoot correctly and if you do not plot every detail ahead of time you can be looking at a painful editing experience.