DV Chromakeys (page 2)

This may be obvious to some, but there are still times, even in the broadcast world, when the subject wears clothing that is the same color as the background. In post, the subject's dress or suit magically disappears. Fortunately, this doesn't result in naked embarrassment, but it does allow the background to show right through them, making them look like a (mostly) invisible person. There are two solutions at this point: reshoot or pay someone to go through the video frame-by-frame and fix the shot. Always direct your foreground subject to wear a color that is completely different from your key background.

And that '80s-style mullet hairdo? Pat it down and get rid of the frizz. Hairs and stray fibers around the outside edge of the subject's sweater do not key well. A good rule to adhere to here is: Keep the lines on your foreground subject simple and smooth. A triangular-shaped Star Destroyer will key over a planet a lot better than a fuzzy space octopus with tiny flailing arms and appendages.

Try to limit your subject's movements as well. A quickly moving subject carries with it a motion blur, where the subject and key background blend together a bit. The worst way to reveal your composite to your audience is a to show a huge colored fringe every time your subject quickly moves. You'll notice this phenomenon even during the weather, when the weatherman quickly points at something. This anomaly is worse in 4:1:1 DV.

Your keying software is important as well. Often, the Chromakey Effect that comes standard with your editor is the most fundamental of keyers, basically only allowing you to select a range of colors to key. More advanced compositing software, such as discreet combustion or the specialized Ultimatte AdvantEdge will give you much better keys. They aren't magic, however amazing they seem, and the fundamentals we've discussed here still apply.

With proper care and a vivid imagination, there are no limits to what kind of spectacular visual effects you can achieve through the magic of chromakeying. Just be sure to wave "Hi" to George Lucas on your way to special effects superstardom.

Mike Kuhlman owns and operates a video production company.

Component Video: In consumer DV, like most professional digital and even some professional analog video formats like Betacam SP, video is recorded in component form, with the brightness or black-and-white portion of the video signal (known as "Y") recorded separately from two color-difference ("Y-minus red" and "Y-minus blue") signals. The resulting picture is clean and free of cross-color artifacts, most noticably the pinkish moire sheen that occurs when, say, black lines going in the same direction appear too closely next to each other. A component video picture is like a window on the world, clear, vivid and with natural-looking color.

If you own a DVD player and a television with component video inputs and outputs, try hooking up each of the three video cables that make up the component color picture one at a time. They are most often color coded green (Y), blue (Cb) and red (Cr). As you connect and disconnect each one, you'll see exactly how each component of the signal combine to make the color picture you see.

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