How to Chroma Key for Broadcast Journalism
Green screens effectively composite two separate images together, and it’s important to know how to chroma key to get the same effects for your production. The most common place you’ll notice this effect is with the weather-person on your news. They’re not in front of a screen with maps projected on it; they’re working in front of a large blue or green screen where the background images are composited. Nonetheless, it’s simpler than it sounds.
Step 1: Find Your Software
Online you can find software (there are many free programs) that you can download to composite images together quickly and easily. Basically, the programs eliminate all the blue- or green-colored screen behind your subject and fill only that area with the other previously shot information, like maps or locations.
Step 2: Set Your Screen
You can find the proper colors for a blue- or green-screens online, and you can buy the screens there (sometimes it’s expensive), or you can purchase fabric or sheets of the same shades and make your own. Remember, the software cuts out all of that color, so make sure your talent doesn’t wear any clothing that is close to that shade. (Note: you may need to determine the background screen color by whether your talent has blue eyes or green eyes, Use the other color.)
Step 3: Lighting
Lighting is critical. Make sure the background screen is not wrinkled at all (this picks up as shadows) and that it is evenly lit. If it isn’t, you’ll get highlights where the screen color comes through rather than the intended composite background. Light your talent evenly, with a soft backlight to distinguish talent from the background screen (if this light is too severe, your talent will “halo”.)
Step 4: Choose Your Use
The key opportunities for chroma key in broadcast journalism are forecasting, on-location pieces and features.
For weather forecasts, have your talent get used to working in front of the screen. This takes practice. It’s useful for them to be able to see themselves with their composited image in front of a monitor. If they’re indicating places on a map, position the monitor next to the camera lens, so that it appears like they’re looking into the camera.
If your talent is supposed to be in a distant location, make sure they’re dressed the part. For instance, if you’re trying to lend credibility to a piece by locating your talent in a distant land, have them dress the way they would if they were really there. (Note: this is just for illustrative purposes; don’t imply that the talent is actually there.)
Step 5: Features
Sometimes in feature pieces, it’s useful to have the talent “lead” the audience through several different locations, as if they were simply “taking a walk.” This adds to the fluid motion of the piece. One thing to bear in mind: any time you add motion – particularly motion that moves across the screen – test your lighting over the distance that the talent will travel so that you won’t get highlights or shadows throughout the entire motion.