Ever wanted to scarf down a baguette at the Eiffel Tower, walk your dog on the moon and add your own five-day forecast to the 10 o’clock news – all in the same day? In the video world, you can do it, no sweat, without leaving your back-bedroom studio. The key is chromakey.
The process is pretty easy, really. Shoot your talent in front of a bright blue or green backdrop, then use your editing software to replace the "key color" with another image, like the picture on a Parisian postcard, some vintage video of a moon-landing or a TV-style weather-graphic tooled in your titling program.
A lot of color-keys look crummy because of a few common mistakes. Here are five rules the pros use to prevent poor-quality keys.
1. Light it Right or it’s Good-night
The first secret for obtaining killer keys is to sufficiently light your backdrop. If you light your green wall with a single lamp you may get a bright green hotspot in one corner and a dark green shadow in the opposite. Put simply: you can’t key out a gradient background. The first secret to good keys is to achieve flat, even lighting so your key color is uniform and consistent. Fluorescent tube lights or large, soft lights positioned at the sides of your weather wall will work well to evenly light your set.
2. Keep Your Distance, Dude
Secret No. 2 is distance. Move your actors as far away from the background as possible and light them independently of the wall. This distance will allow you to position your key and fill lights so that no shadows are cast on the chromakey wall (shadows will not key out) and prevent wall-colored reflections from reaching your subject (colored halo reflections will key out, causing portions of your talent to disappear into oblivion). A strong back-light on the hair and shoulder will help outline the subject for a clean cutout.
3. Slick Down that Hairdo
Bald heads and hair-molds are staples with weathermen for good reason. You’ve got to have sharp edges to get good keys. Curly mop-tops and fuzzy fly-aways don’t key well. Fluffy hair will leave your subject with a key-colored halo that looks laughable. That’s why your local weatherman looks like he’s got a gallon of goo in his hair. He does. The third secret to better keys is to find a bald guy or break out the Dippity-Goo.
4. Be Aware of What You Wear
Make sure your talent doesn’t wear anything that is the same color as the chromakey wall. A television legend tells of a rookie weatherman who showed up just minutes before the broadcast on St. Patrick’s Day wearing a green suit that was precisely the color of the green wall. Unless you want a floating head to deliver the forecast, choose a wardrobe that’s drastically different than the wall. This fourth secret may seem too basic to mention, but you’d be surprised what some people will do if you don’t state the obvious.
5. Be Wary of DV Keys
Mini DV and Digital8 shooters may have trouble getting clean keys because of a pesky technical issue. In a nutshell, the 4:1:1 compression used by the DV format can cause an unpleasant amount of dancing, jagged-edged aliasing around a subject – no matter how good the lighting. The answer may be to use analog footage to perform your keys or invest in a program like After Effects for more keying control. Watch for a detailed technical explanation in an upcoming issue of Videomaker.