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By Bill Schnarr
Ever been at the movies and saw an actor do something that seemed impossible?

Have you wondered how Spider-man could hang from a building one second and be sailing hundreds of feet through the air the next second?

How about Frodo Baggins and his climb up Mount Doom in the Epic Fantasy Lord of the Rings?

Well, the obvious answer is that these actors weren’t doing these things at all. They were making use of a film technique known as Video Chroma Keying.

What Chroma Keying is

Video Chroma Keying is also known as "blue screening" in the movie industry. You may have seen it in action before, where an actor stands in front of a large blue screen and acts out the scene by himself.

Next, the camera operators slip a background in behind him, making it appear that the actor is bounding from building to building or climbing the side of a volcano in an attempt to destroy an evil ring!

Chroma Keying is a feature that comes with many cameras. That means that you can make your own amazing shots and impossible action scenes in the comfort of your living room.

You should be warned, however, that Chroma Keying is considered a skill on its own right. Correctly keying the color you want to use in order to avoid "color bleeding" can be a tedious and time-consuming process. Also, shooting with a video camera (as opposed to still photography) means that this work needs to be done in real-time, making it even more difficult.

Nonetheless, Chroma Keying can be a great way to add a little excitement to your video footage. Are those home movies of your kids turning into hours of boring footage of them playing in the sandbox? No problem! Next time, Key them into an island in the South Pacific, happily building sandcastles while World War Two rages all around them!

The Blue Screen

Chroma Keying is similar to using a Luminance Key. In Luminance Keying, the brightness level is set and all of the brighter (or dimmer, depending on the wishes of the camera operator) pixels are turned off. Then a second image can be slid in behind the actor that shows through where the pixels have been turned off.

Obviously, a Luminance Key is really only useful when creating greyscale images, such as in black and white imagery.

Chroma Keying works the same way, except it uses a color instead of a brightness level. The reason for this is that there are many more variations of color that can be used as opposed to limited black-white or brightness levels.

Traditionally, this color has been blue. Hence the term, "blue screen". A common color these days is also green, but theoretically any color is possible. Blue is most often used because the most common subjects filmed are people, and flesh tones stand out better against a blue backdrop than any other color. Additionally, when color spill or bleeding occurs, blue is easier to cover up than green or another color.

It important to note that when a color is properly "keyed out", ALL of that color will disappear. If your subject is wearing blue and you are Keying out blue, then the blue your subject is wearing will also Key out. This can leave "holes" in the actor where the background will show through.

In fact, this is exactly how Lt. Dan in the movie, "Forrest Gump" lost his legs during the film. The actor who plays Lt. Dan (Gary Senise) wore a pair of long blue socks, and when the blue was keyed movie magic occurred. His legs simply vanished.

Depending on your equipment, editing software or even personal preference, you can decide the color used for yourself.

How Chroma Keying Works

If you are going to step into the world of Chroma Keying, you need a few things first.

You need foreground footage, for starters. Foreground footage is your subject, and your color screen. You also need background footage, which is the scenery that is going to be replacing the color screen.

The color screen needs to be evenly lit so that it is the exact color all the way across. Shadows caused by poor lighting can wreak havoc on the Chroma Key process. Also, be aware of your foreground subject lighting. It is important to have two separate sets of lights, and to have the subject far enough away from the screen that the foreground lighting will not interfere with the screen lighting in the back.

Once the subject has been properly lit and the background color successfully keyed, it is time to add the new background scene.

When these two are placed together, your actor is suddenly transported from a large blue screen to anywhere you want—the only limits are your imagination, and of course, what kind of film you can get your hands on.

Some Tips on Successful Chroma Keying

As mentioned earlier, Chroma Keying is a skill on its own that takes a lot of practice to do properly. When done poorly, Chroma Keying looks really low budget and obviously fake. However, there are a couple things that even a first-time "Chroma Keyer" can do that can improve the quality of their work.

Lighting is the most important part of Chroma Keying. You can never be too careful with it. Take extra care properly lighting your background, and use large white cards to bounce light so that you can achieve even illumination across the entire screen. Remember, different degrees of illumination can create color variations that can confuse your digital camcorders.

Also, be aware of the potential for color spill. You will see color spill as a blue reflection off of your backdrop that colors your subject. In this case, double check the lighting on your subject (again, nice even lighting to eliminate shadows) and then have the subject move farther away from the background screen if possible.

Matte sprays can be attained from your local photography store or even art store. These are useful in reducing the reflective properties of your subject (especially if they have a bald head!) and can greatly reduce color spill or color bleeding.

Editor's note: You may also find a video proc amp (short for video processing amplifier) to be useful in controlling color, matching cameras and so forth for getting the best chroma keying results.

Keeping these tips in mind, you should be well on your way to the exciting world of Chroma Keying. Remember, like anything worth doing, practicing your Chroma Key skills will hone them and turn your boring old home videos or wedding footage into exciting, Hollywood-style action!

About The Author

Bill Schnarr is a successful web site copywriter providing tips and advice about video chroma keying, digital cameras and photography. His numerous articles offer moneysaving tips and valuable insight on typically confusing topics.

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