You can do some pretty gnarly things with a green screen, but you don’t need a high-budget studio to set up your own! Generally either blue or green will work, but for digital video a bright green is best.
Camera shops sell huge rolls for backdrops – we have an 8-foot wide roll for both blue and green at the office – but even this isn’t necessary. Check your local hardware store for tarps – they come in great colors for screening.
You can also buy fabric and create a sheet out of that, but whatever you end up using remember that a matte or non-shiny surface works best. So if you decide to buy some green paint and cover a board, sheet, tarp, or wall with it, make sure not to get glossy paint.
Hang or prop your green screen against a bare wall in your house; it doesn’t matter where you are as long as you can get sufficient and even lighting. Use a light meter if you’ve got one, but if not you should make a visual check through your camera lens and try to get the entire screen as evenly lit as possible.
The more even your lighting scheme, the more consistent your green color will come out on tape or film, and therefore the easier it will be to remove.
Green Screening During Post-Production
Both Adobe Premiere and Adobe After Effects have great video filters for green screening your footage. Regardless of the editing software you use, look for an effect or filter called color key or chroma key.
Using a Key filter like these will let you select a color within your video image and remove all pixels of that color, within a certain threshold so that colors close to it on the spectrum can be removed as well.
Sometimes I find it helps to use multiple key filters, especially if my lighting hasn’t resulted in a fully consistent green throughout. Select pixels closest to your person (or subject, if it isn’t a person) to get the cleanest effect.
By keying out shades of green closest to your subject, you may find that there’s a ‘flickering’ effect around the edges of your video where other shades of green are getting through. You can use a tool called a garbage matte to clean up your edges.
To use a garbage matte, apply the tool to your video frame and then drag each point inward from the sides and corners, until you have eliminated most of the outer portion. The matte automatically makes everything outside itself transparent and keeps everything inside visible.
Even if you have used great lighting and have done a thorough job keying, you might still notice a green ‘halo’ around the subject as it moves. Sometimes this is a ring of green, and sometimes it’s as subtle as a greenish tinge where the background reflected itself onto the subject.
You can use a desaturation filter to take the color out of the halo and turn it to white or gray instead. It will still be there if you look closely, but at the very least it should reduce the visibility of the halo and help it to blend in with whatever background you throw behind it.
With your keying, matte and desaturation complete, you should now have a layer of transparency in your video. If you put another video or image on a layer beneath it, you should be able to see through those areas. If not, you did something wrong. Go back up to the top of this page and re-read it.
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