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In this chapter, we're going to look at keying and compositing. Keying is the process of removing a green screen so you can isolate an object. So if we wanted to composite this bounced basketball in another scene and not in front of this green thing, then we would shoot it in front of a green screen and then remove the green screen and then we could adjust it later in post how we like it. Almost always, the first part of the process, when you're keying, is to create something called a Garbage Matte. If we do a search for the word Garbage in the Effects panel, we'll see there is actually several different effects for this, as you could see that there is an Eight-Point, a Four-Point, and a Sixteen-Point Garbage Matte.
Now what you do with the Garbage Matte is you get rid of the junk that wound up in the scene. Invariably, when you're shooting green screen work, there is a boom stand or there is other technical stuff off in the distance because the green screen didn't quite fill the entire screen. In this case, there is a little bit of the floor and some tape, and so, we need to get rid of that before we key the footage. We get a much cleaner key by getting rid of that junk initially by creating a Garbage Matte. These effects are actually really cool for that. We'll start out by applying the Four- Point Garbage Matte and drag-and-drop that into our footage.
Then the best way to fiddle with these is to click on the effect to highlight it and then you'll get these control points and you can just click-and-drag to remove objects that you don't want. So we can click-and-drag, like this, to get rid of the bottom. Now this will be so much easier for our Keying tool to go in and look and just see the green to get rid of the green. It won't have to worry about processing all of this junk as well. Now we could also open up the effect and adjust these manually, so even though my Bottom Left effect point is off the screen, I could adjust that by fiddling with these controls here.
I want to hold the Shift key to move that a little bit more quickly, but you get the idea here. I'm just going to select this effect and delete that. As you can imagine, Eight-Point and Sixteen-Point are just the same exact thing, except with more points. Now be aware that you're going to get more smoothness with something like the Sixteen-Point Garbage Matte. If you are moving around a character, it might be a good idea to have more control like this. But oftentimes with a Garbage Matte, you have to animate it just in case something kind of moves out of frame.
So let's say, we had a person here and maybe we moved all of these points around the person, and then when the person moved their arm, we have to animate these points to encompass their entire frame. So it might be easier to do that with less points. For what it's worth, I typically find myself using the Eight-Point Garbage Matte most of all. I find Sixteen-Points to be too many and I find Four-Points to make things little bit too blocky, Eight-Point seems like the goldilocks, just rightness, where it's like right in the middle of the two.
Now just to be clear, before we close out this movie, with the Garbage Matte we're only trying to get rid of this extraneous junk here, we're not trying to remove the green screen. Although, if we know that the object, the subject that we're trying to key out is - never goes in a certain area of the frame, and there's nothing wrong with moving those garbage points there. So if we move this basketball in time, for example, we could see that it never really goes right here. So we could do this if we wanted to, to remove more of that green screen, actually, it does go right there, somewhere around there, where it just barely avoids the bounce so we could move this down a little bit, like that if we wanted to.
But you want to make sure with your Garbage Matte that it stays clear of the subject at all times, so this is a no-no, how it cuts off the subject. So we want to make sure that our subject is never cut off and all of the extra junk is. Then once you've created this initial Garbage Matte, you're ready to actually apply the Keying software, the Keying tool to remove the green screen.
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