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In this movie, we are going to look at how to remove a green a screen background. When doing a film and video work oftentimes as subject is filmed in front of a green screen, such as this podcast host here. And then in postproduction in After Effects we remove the green screen to place them on a different background. That's exactly what we are going to be doing in this movie. This process is often referred to as keying. You might hear somebody say I am going to pull a key, or I am going to key out this background. So the word key is used as a noun and as a verb. So, what I'm going to do is I am going to apply perhaps the best keying effect in After Effects called Keylight.
I am going to apply this to the top layer the podcast, part 1.3 clip here. Nothing happens at first. That's okay. That's normal. And what we are going to do is go over here to Keylight and there is this Screen Color property and we are going to click the Eyedropper tool and then we are going to click the green screen background. And instantly we get some pretty cool results. Now if we take the View dropdown from Final Result up to Status we'll see that the final results are not quite perfect.
You see Status shows us what is completely transparent and what is completely opaque. Gray pixels are semi-transparent, white is completely opaque, and black is completely transparent. So ideally we want the background be completely black and are subject to be completely white, neither of which is the case. So, what we do is we open up Screen Matte while looking at the Status view and we are going to increase the Clip Black value until the black is completely gone. And then we are going to decrease the Clip White value until the subject is pretty much all white and we do want a gray halo around the subject.
That's completely okay. Now if we take this view back to Final Result we see that we have an even better key here. Now in full disclosure, I should tell you that keying is almost never this easy. This video here of this subject was filmed by video people at lynda.com, their in-house video people. And they are unbelievably talented and they are extremely skilled at what they do. And a lot of professionals even that work with green screen all the time do not set up a green screen that good and a lot of things contribute to the way a green screen turns out.
A lot of times like video compression, if you have like a standard DV hand-held camera that compression will make the green screen look terrible. Bad lighting will make it almost impossible to get a good clean removal of the background. Video compression as I talked about, the different way that it's compressed. This is a very lightly compressed footage so it turns out really good. The color space with a camera also contributes to the final result, and so we had a lot of really great benefits working for. So, another that you'll have in most green screen footage is like a boom mike or some other garbage hanging around in the screen.
So, what you typically do in a professional workflow before you key a piece of footage, you create a mask called a garbage matte. So, I might select the Rectangle tool and click and drag a mask around our subject and that would get rid of all the other junk that's around here and it would help the keying tool, in this case Keylight, to be able focus on the area that really matters most. Of course, you want to make sure that as you scrub your timeline that the subject or the talents never moves their hands or their body outside of that mask, because it will appear to be chopped off.
But this is how you pull a standard key if you've got some really good footage to work with. Now there are certainly tweaks. Number one we could select the Selection tool and click and drag and move our subject over, and that makes things look pretty snazzy there. We also might scale them up or down or what have you, and another thing is compositing. We want to make these two shots look like they belong together and everybody who sees this virtual set in the background knows that he's not really there. Nobody thinks that there is some huge TV studio setup with this gargantuan TV and then someone happens to be filming at that spot that's somehow on the beach with palm trees.
But it still would help if we had these colors of these two layers matching a little bit better. So, as we go through, and we start talking about keying a little bit more, we're also going to start talking about compositing in this chapter, and that's basically taking these different elements and combining them and making them look better together. In the next movie, what we are going to do is talk about how to take bad green screen footage and refine it with a new tool in After Effects CS5.
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