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This month we’ll talk about green-screen effects. Whether you know it or not, you see it all the time on TV. It’s regularly used in news studio rooms and is most widely known with presenting the weather on TV.
Basically, the presenter is performing in front of a green background. This green background will be removed (digitally) and replaced with an alternative background.
A quick example of a green-screen setup (taken from Google Images) is shown.
This end result will look a bit weird, but I want to keep the full setup in the shot to let you see exactly what is/isn’t being removed.
SETUP
The first thing we need to do is import our green-screen recording. In this case, I’m using a static image, but it could easily be a video. And then drag it to Video2. It must be Video2 as the background will be Video1. In other words, below/behind Video2.
I then import the image/video that will be the new background.
CHROMA KEY
I right-click on the green-screen clip in Video2 and choose Add Effect > Alpha Manipulation > Chroma Key.
If your green-screen video is still selected (red outline), you’ll see the Chroma Key effects in the Properties tab.
It will look like nothing has happened, and nothing has happened yet. Click the water droplet above the Variance number. This will let you pick a colour in your video. Obviously, you click on the green.
The Variance value is how precise (or not) the masking should be. Lower the value and more green will show, higher will begin to wipe out parts you want to keep. You’ll need to find the sweet spot for your video/image.
Black is probably replacing green in the image, but that black is actually transparent.
THE SWITCH
Drag the replacement background image/video into Video1 and you’ll see the transformation.
You’ll probably have to adjust the Variance slider a touch once the new background is in place. If the Variance is too low, you’ll see a green fuzz around the presenter’s outline. Too much Variance and the presenter will have a hard sharp, jagged, outline.
CONCLUSION
The single most important part of this is that the presenter (in this case) must not be wearing anything green, or reflective. If, for example, the presenter is wearing a green dress, or a green tie (even of a different shade of green), then those items would become transparent. If their clothing/accessories were reflective, then they may end up with green reflections on them which will also become transparent.
I’ve botched together an edit of the original image to show the presenter in a green dress (right).
Even though it’s a different shade of green, it’ll still be included in the chroma key effect (far right).
Obviously, in some cases, that’s what you want. Some movie shots will have crew entirely covered in green to easily erase them. Same with wires and props.
Don’t forget to add me to the credits of your next big blockbuster!