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In working with green-screen footage you'll find that there will be plenty of occasions where you'll need to actually use masks to aid in the process of cutting out your subject from its background. Now I want you to understand there are two different kinds of masks that you can create to help with this process. In this example here, you can see we've got our subject and a beautifully lit green-screen background and if we press the spacebar, we can see that it's an interview and she's talking, but she's not jumping around the screen or anything like that.
If you look over on the side, you can still see part of the studio. This is quite common. A lot of times you may not have the time, the space, or the budget to actually have somebody rent a full-screen green-screen studio, but that's perfectly fine. As long as you can get a piece of green that's just large enough to fit behind your subject, you can pull a beautiful green screen in Motion and actually use masks to create something called a garbage mask, which is the first out of the two kind of masks I want you to learn about.
So first thing, let's go ahead and key her out of the background. Select the Video layer and go to the Library. See in Motion when you're going to be combining keys as well as masks, you want to make sure to apply the Keyer and adjust the Key settings first before you add your masks. It's just how Motion processes things, and it's the recommended workflow. So I'm going to take the Keyer and drag and drop it right onto this piece of footage, and sure enough she is keyed out of the background. Now we can see all of our other footage that's moving around, so I'm just going to turn off the footage that we have from the other day. And I'll leave this background on for now, but obviously you can see you know we could put whatever background want in here.
Now I could go through the Key settings and make adjustments like we've gone through extensively in the previous videos, but this is about masks, so let's add a mask to this clip. Now before we do that, I want you to select the video layer and then come down to your toolbar. Just to the left of the timing window choose Rectangle Mask. Now you could choose any of these masks, but since she's not really moving around, you can just use a simple rectangle mask. Make sure to draw a rectangle large enough around the subject, so as she continues to move, she's not going to get cut off by the edge of the mask.
So when I let go here now you'll notice the edge of that mask is cutting off the extra piece of studio that was there. So if we press play, you'll notice she's moving right along, and we don't have that extra piece of studio. Now if I select the footage here, you notice it disappear just because the length of her clip was only four seconds and the length of the entire compose a little bit longer. So before we move on, let me show you what would happen if we actually turn off the key. See when I turn off the key, only the area that I drew with a mask is now visible in the scene.
So even though I applied the key first, it really doesn't matter because the mask is cutting off a section of the image and the key is cutting off a section of the image and they're both completely independent of each other. So if I wanted to, I could actually keyframe the position of this mask, or I could apply this filter to another clip that we shot with this person, but you get the general idea. Now that's how we create a garbage mask, but let's turn this Video layer off by a collapsing the layer and turn off its visibility.
I want to turn on this next layer here. Now you may recognize this from the previous videos. If we go and scrub with our playhead here, you'll notice there's a large section that's missing out of the key. So if we open the disclosure triangle for the video layer and disable the green-screen key, you'll notice her T-shirt did originally have a big green circle on it. Now obviously, if you know you're going to be shooting somebody on green screen, you want to make sure that they don't wear any green articles, but as everybody knows, more often than not things typically don't quite happen the way you are expecting during a production, so sometimes you'll have to "fix it in post." So let's do that.
Enable the Keyer, and now if we go down to our Mask tools, go ahead and choose Circle Mask and make sure we have her video layer selected and just draw a circle mask. And actually, I'm sorry, I should have selected this first and then gone down to grab the mask, but you can see now we've got the video layer selected and our Mask tool selected. So if we click and drag, you'll notice, well, the mask has cut or out, and that's not exactly what we want to do, so let's go to Mask settings in the Inspector and change the blend mode from Add to Subtract, and that's still not what we want to do.
We could try Replace and Intersect, but really those are designed to function when you have more than one mask on an object and since the key isn't a mask, these won't work either. So what you need to do to create a holdout mask--okay, this is the second kind of mask that we're to be talking about-- what we need to do is actually start by deleting this mask-- okay so we've our original video footage--and duplicating this keyed footage. So with it selected just press Command+D under keyboard to duplicate that layer.
Now we can delete the key off of this upper layer just by selecting the Keyer filter and pressing Delete in the Layers tab, and now we can go down and grab our Mask tool can create a circle mask around our logo. I'm just going to go ahead and click and drag to draw the circle, and now check this out. It works perfectly, because this video layer now is only this one circle. See if I solo this layer by pressing Ctrl+S, you'll notice the mask is cutting out this one area, but since it's over top of this other layer, if I press Ctrl+S, you'll notice this layer has the key on it and we have our holdout mask on the layer above.
So obviously this is moving footage, so if I press the spacebar to try and play, you notice this isn't quite working, what you need to do is animate the mask, so if we move our playhead back to kind of where we created the original mask, here we go, we can animate the mask by selecting the mask itself, going down to our Transform tool, and make sure we have Edit Points selected. Now with Edit Points selected press A on your keyboard to turn on automatic keyframing.
Now just click on one of points to set your first keyframe for the control points. Notice how it automatically created the keyframe here. Now to be very precise, what you can do is actually move up and down the timeline. So I'm using my right arrow to move down the timeline. So I'm just going to keep clicking until I know this mask isn't working. So now I'll just move this control point over and adjust the mask accordingly. So if I use my arrow keys to move back through, you notice now the mask is tracking along.
This process is actually called rotoscoping where you're going in and cutting out a specific area of an image, but since we're using this as a mask on the duplicated layer, we are rotoscoping a mask to create a holdout mask. So when you go to create your masks combined with keyers, just pay special attention so you can determine whether or not you want to create a garbage mask or whether you want to create a holdout mask. And by all means, if you think you're going to be animating your masks, make sure to pay attention to whether you have Automatic Keyframing turned on.
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