I always get emails about how to get a good key on a green screen (especially on a budget). First off, I should mention that we shoot the Mac MediaCast on a green screen. Our format is DVCPro HD — if you can shoot in HD, that’s half the battle, because Standard Definition DV footage gets its small file size from compressing the color information. This makes it more difficult to get a good key.

Here are some tips on how to get the best green screen key with a DV signal in Final Cut Pro:

1. Light your green / blue screen as evenly as possible.
This is the most important step. It should appear as closely to “one color” to the camera and Final Cut Pro as possible.

2. Light your subject well.
This includes a good strong keylight and a backlight to help the subject “pop” off the background. For more information on this, do a Google search on “three-point lighting”. I thinks it’s common sense, but I should also mention that if your subject is on a green screen, they should not be wearing green.

3. Prep the Video
Once your video is shot and in Final Cut Pro, crop the image to just around the subject to get rid of as much of the green screen information as possible. The less green there is to key, the easier it is to key. If your subject is a person, beware of arm movements, etc. that would go outside the crop area.

3. Keying Plugins
In Final Cut Pro– use this “cocktail” of plugins:

Color Smoother 4:1:1 — this “preps” the DV image for keying by attempting to correct some of the difficulties introduced by the DV colorspace — as mentioned before — DV gets its compression by leaving the Grayscale (Luma) portion of the image high res, and by pulling extra info out of and compressing the color portions. That’s why keying DV is so difficult.

Keying Plugin: This can be the Blue and Green Screen plugin, or the Color Key plugin. Use whichever you’d like. I, personally, use a Color Key plugin from Boris that I feel is more powerful that the stock Final Cut Pro plugin. Don’t mess too much with the Edge Thin or Edge Feather until the next plugin–

Matte Choker: This has better Edge Thin and Edge Feather settings than the keying plugins. Make your settings here and then go back to the keying plugin if you need to fine tune. Again a 3rd-party plugin, such as from Boris, will work well here.

Spill Suppressor Blue or Green: This helps get rid of some of the difficult artifacts that hang around the subject.

And here’s the most vague advice of all– just mess with those settings until you get a good key. : )

Remember to do this plugin work with your subject sitting on the actual background you’d like to use (i.e. your fancy computer backdrop or stock beach image or the Eiffel Tower). If you’re ONLY viewing the alpha channel (showing up just as black or checkerboard in Final Cut Pro), you’ll end up being pickier than you have to, because there will always be some artifacts.

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