Your Assignment: Grab Shots for Compositing

Most of the tasks in this hour will involve creating transparencies in clips by removing certain colors or luminance (brightness). To best see how that works in the real world, you need to grab your camcorder and tape a few quick shots.

Normally for images that you intend to key, you'd need to have your camera absolutely locked down. No camera movement at all. In this case, because it's just an experiment, don't worry too much about that. But once you see how much of a viewer disconnect there is when a keyed object bounces around over a keyed in background, you'll see why a rock-steady camera is critical.

Here's your assignment:

• Videotape an inanimate object ”preferably a smooth object to minimize shadows within it ”in front of a solid color. That color should be distinctly different from the color(s) of the object. Otherwise, when you later "key out" that background color , similar colors in the object will turn transparent, too, leading to some odd results.

• Tape a person talking or moving in front of a solid color background. The best is sky blue because that's complementary to skin tones. Just make sure your subject's clothes don't have colors that match or nearly match the background. Most production studios use so-called chroma blue (or green ) screens. I'll highlight the advantages of each in a sidebar later in the hour.

• Tape a dark object in front of a lightly colored surface (white is best) and a lightly colored object in front of a dark backdrop. Try this with a person as well. The greater the contrast between the subject and the background, the easier it'll be to make the background transparent.

• Tape a distinct background with nothing moving in it ”that is, no waving palm trees or soaring birds. Then, without turning off or moving the camera (this is the one exercise when you need a rock-steady shot), have someone walk into the left side of the scene, stand around for a while, and then walk back out the left side. Have that person do the same thing entering from the right side and then walking out to the right. For a bit of comic relief, have your "actor" wave toward the center of the scene before walking off camera. You'll use this in the next hour to create split screen and difference mattes, but you might as well shoot it now while you're at it.

• Finally, grab a few shots of background locations in which you'd like to place the objects/people you've videotaped. You will later key your subjects onto those locations.