5 Secrets to Pulling Off a Hollywood-Level Chroma Key (Besides Good Lighting)

Director/Cinematographer Matthew Rosen shares with us some of his "secret" techniques in the video below. And trust us -- there's no talk about how to light for chroma key. We promise.

Choose the right chroma color

Chroma green is typically the color filmmakers choose when the decide to do some compositing, but not necessarily because it's better or worse than blue (or any other color). Though there are plenty of technical advantages to using green, your choice should be based on the qualities and obstacles of each specific shot you're capturing -- and most of the time blue is found in the shot more often than green. Here are some tips Rosen points out:

• If there's green in your shot, choose a blue chroma color. If there's blue in your shot, choose a green.
• Green is twice as reflective as blue, so it tends to contaminate your shot more.
• If your background is blue or green, use those respective colors for your key color.
• Most modern cameras have sensors that use the green channel to carry luminance, so shooting on a green screen could result in twice as many pixels.

Don't overexpose the chroma screen

You're gonna need to watch this part of the video to get a good explanation on how and why you need to expose shots differently for chroma keying, because I simply can't give you one. (Lots of percents, RGB parade talk, and zebra stripes.) Simply put, a healthy exposure for a typical image just won't cut it for chroma keying -- it'll be overexposed.

The cleaner the screen, the cleaner the key

Other than green or blue fabric, the next most important tool to have on you when chroma keying is an iron. Seriously -- or whatever it is that will help you flatten those creases and folds in your screen. And I KNOW we said that there will be no talk about lighting, but you can't really talk about having a flat and even screen without mentioning that lighting plays a major role in making it that way.

The less you compress, the better the key

This is simple: using a format that compresses your video less, like RAW or ProRes, will result in a better key, because it retains the minute details of your image. 

One-click keys

Essentially, if you've done everything right -- you've chosen the right chroma color, exposed correctly, shot against a clean screen, and chosen the highest possible compression format you can -- you should be able to isolate your chroma color in one click when you begin the post process. See, every aspect of chroma keying is important, because they all influence the final result. A one-click key means you put in the work to do it right the first time and avoided the "fix it in post" nonsense.

Do you have any "secret" tips on how to pull of a pro chroma key? Let us know in the comments below!

Source: KINETEK