Chroma Keying for Cheap
Chroma keying is a special effect which allows your movies to go to places that otherwise would not have been possible. Originally, this was a technique only available to big budget movies due to the equipment needed to pull it off. But, now anyone with a decent editing program on their computer can effectively pull it off. You also don't need a giant sound stage for your green screen anymore either.
Chroma keying works by isolating a specific color in the video that then becomes transparent. A green screen needs to be a uniform color that will stay uniform when lit.
What Won't Work
The walls in your parents living room might be green, but that paint is going to have some shininess in it that will cause it to be fifty different shades of green when lit. That's no good. You might also consider using a green sheet, but you should avoid that if there's a better solution. The stitching in the sheet might not be that thick, which will allow light to spill in through it. The result will be a green screen that's not completely green and that can cause some headaches.
Step 1: Renting a Green Screen
If you're going to use a green screen, then you should do it the right way. The cheapest thing to do is to rent a green screen from a rental house. They come in sizes that range from 6' by 6' to 20' by 20' and can cost anywhere from $50 to $150 to rent. These green screens are going to be uniform in color, and they won't reflect light so they stay evenly lit. They're also thick, which means that light won't spill through them. What you do is a set up a rig called a goal post. It's a piece of pipe attached to two stands. You tie the green screen off to the pipe and raise it into the air. You now have a green screen to work with.
Step 2: Painting a Green Screen
Another alternative is to paint your own green screen. It is possible to buy chroma key green paint. This color is the same as green screens and will not reflect light. You may have to special order this paint if it's not available where you live, so plan accordingly.
Step 3: Lighting a Green Screen
The most important thing to pulling off this effect is lighting the screen properly. The screen needs to be evenly lit so that there is only one green color instead of ten shades of it. A poorly lit green screen is very difficult to key out. You want to keep the lighting from the green screen off of the subject. Instead, the subject's lighting should match the lighting style of the video that they will be keyed into.
Step 4: Post Production
Chroma keying used to only be possible with expensive video equipment. Now, anyone with an editing program on their computer can do it. If you have a program like Avid, Adobe Premiere or Final Cut Pro, then you will be able to pull off this effect.