How to Avoid Mistakes when Chroma Keying
Chroma keying is a wonderful special effect that can take your movies to places that would normally be impossible to go to. You can convincingly set your movie in space or under the sea. If you know what you're doing then the only restriction is your imagination. So much media today uses chroma keying. The weather report on your local news station uses chroma key as well as the latest big budget Hollywood movie you've just seen. Because it's so common everyone thinks that it is easy to do. But there are a few mistakes that can be made which will ruin the effect.
Using a Poor Green Screen
The first mistake you can make with chroma keying is using the wrong type of material for your green screen. For example, using green paint that you bought at the hardware store to paint a green wall is a big mistake. If you're going to paint a green screen then you need to use real chroma key paint because it is matte paint. This type of paint absorbs light and stays flat instead of having an ugly shine. Chroma keying is all about taking a specific color and making it transparent. In order for that to happen, your green screen needs to be uniform in color and chroma key paint is one way to get it right.
Of course you don't need to paint a wall for a green screen. You can string up a green screen cloth for your effect. If this is what you're going to do then you need the right material. You can buy green screens at professional video equipment stores or you can rent them. It's important that you use a green screen meant for video and don't be cheap by using a green sheet. Sheets aren't as tightly sewn together as the green screens which allows light to spill through them. That makes the overall color scheme uneven and useless. Use the right materials for the job.
Poor lighting is another common mistake with green screens. You need to evenly light the green screen so its color is consistent throughout the shot. It needs to be one uniform color and not multiple shades of green. Otherwise you are going to have a lot of headaches in post production and might even have a very poor looking special effect with green halos around the actors.
Mismatching the Lighting
Chroma key lighting is done in two parts. One part is lighting the green screen and the other part is lighting the actors. When you light the actors you need to pay close attention to the lighting of the video that will replace the green screen. You have to motivate your lighting on the subject so that it matches the other shot. This way the subject blends in with the background instead of having opposite shadows from it.