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The first step in the keying process is to pre-process the green screen or the blue screen, to set it up, or sweeten it, for the Keyer. I am working with these two pictures here, the boy and the boy background. If you'd like to load those, you'll find them in your Project Media, the boy folder. There he is. We've got 12 frames at 1K resolution, and the Boy background folder, another 12 frames at 1K resolution. Okay, like we saw in the overview, we are going to create a separate branch of the compositing Node Graph right here that is specifically designed for pulling all the keys.
And then we will use a separate branch over this way using the original green screen for the actual compositing and color correction. So one of the first things you want to do for pre-processing it would be something like doing a degrain operation. So I am running NUKEX so that I have the Denoise node here. So I am going to bring this in, scooch into my picture, come over here and sample the area of the screen in order to get some denoise going on here. And just to show you how effective this is, I am going to gamma down the viewer and then gain it up.
So I can toggle the Denoise on and off, and you can actually see the green come and go. The big issue for degraining is you want to remove the grain without softening the edges. Of course, you can use any degraining technique that you might have handy. So we'll toggle that back on. By degraining it, we not only remove the sizzle that might be in the edges, but it also helps to eliminate pinholes from the green. I am going to re-home the viewer and clear the Property bin to go on to the next step, which is garbage matting.
Garbage matting is a critical part about the pre-processing. So let's add a roto node here, and then I am going to draw my shape here. All right, then, I will go to the Shape and invert it and then turn on the Eyedropper node to sample the green screen so I can get a matching green right there. Re-home the viewer, and I am going to turn off the overlay, so we can see the edge.
Now, you don't want a sharp edge like this, so I like to take all of my Beziers and add a little feather, like maybe 10. And this way we don't have a sharp edge on either side of the garbage matte. If you leave a sharp edge, sometimes the Keyer will see it. The main purpose of doing the garbage matte is if I turn it off, you can see we have these nasty dark edges. And if you try to adjust the Keyer to get rid of those, you have to hammer the key far too much. So we would much rather just have to key this area right here and get the rest of this as a freebie from our garbage matte.
Now there might be other things that you could do to pre-process the green screen. You might have to re-register the channels if they were out of alignment or suppress highlights or any other operations that are designed to help the Keyer pull a good key. And again, we are going to be pulling our key on a branch right here, whereas we are going to keep the original green screen to use for the actual composite. Now that the pre-processing is done, we are ready to start pulling our keys.
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