Going Transparent: Chroma Key Tips for Everyone
It’s been a long time since I’ve gotten to work with green screen. But one of my latest clients needed a virtual spokesperson video, and chroma keying on a green screen was the call. Back when I started working in video, green (and blue) screen work was incredibly difficult and usually produced pretty horrible results. Fortunately, today’s tools have made things a bit better. Here are a few things I learned about working with green screen to produce high quality chroma keys.
- Use a light meter. Making sure your subject has the same exposure reading as the green screen is important in getting a good, clean key to pull.
- Eliminate all shadows. Shadows on the green screen are a hassle in post. Try to eliminate (or at least mitigate) as many as you can.
- Use a large enough space to get separation. Related to #2, get your subject away from the backdrop so their shadow doesn’t fall on it.
- Clean your lenses…all of them. Smudges, streaks, splotches, grime and dust all make for a really difficult chroma key. Clean all your lenses, filters, and–if you’re using a TelePrompTer–the two-way mirror.
- Get the proper white balance. If green doesn’t look green when you shoot, it’s not going to look green in the edit suite either. Which means it’s going to be a pain to color correct then pull the key.
- Ensure super sharp focus. If you’re using traditional video camera with a non-moving subject, do a deep focus and mark the spot on the floor and the camera. If you’re using a DSLR, use the camera’s digital zoom do focus. Zooming the lens on a DSLR will throw the image out of focus when you move it.
- Use markers. If you have movement in your chroma key shot, you’re going to want to use tape markers to maintain focus and help editors in post. Markers on the floor for talent (and focus pullers/camera ops) allow you to know exactly where the focus point lies at a particular point in the movement. Markers on the background will help motion artists to track camera movement.
- Record at the highest bitrate you can. While high bitrates aren’t necessarily going to make for an easier time keying, the better image quality can help pull a sharper key with more detail. You’ll also avoid the “jaggies” that result from high compression/low bitrate.
- Watch your audio. With all this activity centered around making sure everything is perfect for the chroma key, it’s easy to forget about one of the most important parts of any motion picture production: the audio. Check your mics, make sure they’re working, and listen for ambient sound that might interfere with production.
Watch for an upcoming post about why most productions use green screens instead of blue, and when blue screens are appropriate.