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So inevitably, you'll have a client that asks you, hey, can you put this piece of footage over a different background? And you'll go, sure, did you shoot it on green screen? And they'll look at you and go, what's green screen? At which point, you'll have to look at the footage and determine whether or not you can fix it with a Roto Brush, before you tell them no. But in all seriousness, the Roto Brush actually can help save you in some of those situations. So for example, in this piece of footage right here, you can see we have this sunflower and we have this nice blurry background.
Now this is a pretty good representation of a scene that you should be able to use the Roto Brush to isolate this sunflower from its background. So to do that, we need to get started using the Roto Brush. Before you load up the Roto Brush, you need to make sure that your Fast Preview Options are set to Off. The Roto Brush doesn't particularly like Adaptive Resolution so let's change that to Off. And now to load up the Roto Brush you need to double-click on your layer, so you can open up the Layer panel viewer.
Now I'm just going to expand the viewer, so we can see the entire piece of footage. Now the Roto Brush is this tool up here on the right-hand side of your Tool palette in the upper left corner of the interface. It looks like a little guy with a paint brush. Go ahead and click on that. If we scrub through our scene, you should notice, okay, the flower is dancing, that's great! But the exposure in the general shot never really changes. A lot of times if your footage changes, you may want to start from a later point in the timeline to where the foreground and the background object are most different.
But right now, since this isn't changing very much, we can go ahead and just start at the beginning of our project. Now that we're set at the beginning, what you want to do with a Roto Brush is click and draw inside the area that you want to keep. So notice I'm not drawing all the way out to the edges. Part of what the Roto Brush does is analyze the image and determine exactly how far out it wants to be in order to create that selection. So notice that it did a very good job here. For the stem, I'm going to use a smaller brush.
Now a quick key command you can use for any painting in After Effects is to hold down the Command key and left click and drag up or down. So up, it makes it larger, down, it makes the brush smaller. On the PC you want to use Ctrl. Now as I'm dragging down here, again, notice I'm not going all the way out to the edges. I'm just selecting the main portion of the image that we want to keep. For larger areas like this, again, I'm going to Command+Left-drag and just drag up and draw, there we go.
Okay that one is looking pretty good, and I'll make this brush a little smaller for this side and there we go. When I drew this, notice in this area down here it accidently drew too much of the information. The first thing I recommend doing when this happens is just pressing Command+Z or Ctrl+Z to undo that last stroke. Sometimes you can just choose a smaller brush and then redraw the stroke to see if it interprets it properly the next time. Now if it doesn't, just like this, you're okay.
There is another way to refine the stroke. Now if I hold down Option before I start drawing, notice my brush is changed into this red circle with a minus symbol. See the green plus means, I'm going to add to the stroke, when I hold Option or Alt on the PC, it means I'm going to subtract from the selection. So now I'm just going to draw outside the area of the leaf making sure not to draw into the leaf. Okay, perfect! Now it's actually refined the edge of what we were doing.
This looks pretty decent. You can refine the edge of this right here with a Matte tool. So for example, if I wanted to smooth out the edges, I could just increase this number a little bit and wait for a second and it will smooth this out. Now here let's just crank this up quite a bit, so you can see exactly what's happening here. See how the edges are kind of rounding out? So we don't want the Smooth set to that high, let's just set it to around 3 or 4. Now that will smooth out my edges.
If we press Page Down to move to the next frame, you can see it's doing a pretty good job of tracking what's happening in the scene. If I press Page Down again, it's still working. The way you want to work in the Roto Brush is to literally work frame by frame just pushing Page Down and seeing how well it's tracing the object that you're trying to isolate. Now I want you to look in the lower left corner of the Layer Viewer. You see this yellow square? That's letting me know, that's the first frame that I set up for my Roto Brush, and then this area with the pointing arrow kind of icons, that let's you know that anytime I make any changes to the right side of this yellow frame, those changes will propagate down the length of this preview area.
As I am pressing Page Down here, notice up here in the upper portion of the Layer panel, I have this one area that is not getting cut out. Most of the time I would fix that outside of the Roto Brush, but I want to show you what happens if you refine the edges of a selection. So let's zoom into 100%. I'm going to press the Spacebar and click and drag with my left mouse button to just grab the Pan tool and move up in the scene. Let's make a very small brush, I'm just holding down Command+Left-clicking and just click inside while holding down Option.
And now we got a red icon and we can just click and drag in this window, and notice now it's created a new selection. Now our preview area has continued to grow. As you make these cursory changes to the brush, that changed for those extra areas. So if I just Command+Z to undo that, notice you can see there is the shortened area. If I go back up under Edit > Redo now it's going to propagate further down the timeline.
Another tip with using the Roto Brush is to make sure that you use as little paint strokes as possible to make adjustments in your frame. Everytime you draw a paint stroke and it's incorrect or you've made an adjustment, the Roto Brush will record that stroke. So that's why I've been very particular when I've made an incorrect stroke to press Command+Z and undo. That will not save that stroke, so that way when I make my adjustment, that stroke will propagate throughout the length of this area.
Here let's switch our view back to Fit up to 100%. The idea with the Roto Brush is to literally go frame by frame as you're painting and make adjustments using the Add to Selection option, just by left clicking and dragging with the green icon, or holding down Alt or Option to select less of an area. I'm just going to move to the end of my propagated region here, which is about one second, and I'll press N to end what we've done so far, because I think you understand the process.
You could continue going down frame by frame and refining your matte, or not refining your matte. Let's see the results of what we've done up to this point, which is only the first second. I want to load up a RAM preview, and in my Preview panel let's deselect from current time, that way the RAM preview will always load from the beginning of the comp. When you press 0 on your keyboard, notice now I'm going to get a preview of the Roto Brush and up here in the info window, it told me the Roto Brush was propagating.
Now notice that one corrective stroke is popping into the Roto Brush selection at the specific frame where we first painted the Roto Brush. Now I'm going to stop playback here for a second. As the Roto Brush is moving, the edges of the matte are moving, so there is a way to refine the edges of the Roto Brush. But we are going to jump into that in the next video.
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