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Now if you're joining me from the previous video, you know we've cut out this flower from its background by using the Roto Brush. So we're going to continue with that because creating the selection is only the first part of the process. Let's double-click Layer 1 to open up the Layer panel and reset our magnification to Fit to 100. Now let's resize the interface to make the timeline a little smaller and give us a little bit better view of the scene we're working in. As you preview how the edges are working within the Roto Brush, it's a good idea to actually set your magnification to 100%.
Now within the Layer comp window down in the middle, you can choose whether you just want to look at the boundary of the edge of the Alpha channel that we're creating, or an overlay of the selections that we're making, or if you click and hold, you can go up to Alpha and it will show you the edges of the matte. Now let's go ahead and load up a RAM Preview, so you can see the edges of the matte. Notice how the edges are kind of wiggling around. That's happening because of the movement of the flower. But that movement is actually called Edge Chatter.
So if we stop playback here for a second, we can open our Effects Control panel - I'm just going to go up under Window and choose Effect Controls, and on the left-hand side here we have a bunch of matte options. If we look at the matte options you can see we can smooth the matte, which we went over in the last video, but I'll just show you here for recap. If you crank it up, notice it makes the edges smoother. But that has a bad habit of actually giving you a really poor matte, so let me just undo that. That works well if you're trying to use the Roto on something that's rather blurry.
You can choke the matte just by bringing that number up or down. So obviously to the left, actually it does the opposite of choke, which gives it more room, so just understand that. Refine Matte is what we want to look at. So select Refine Matte and the first option is Use Motion Blur. Go ahead and select that if your image has a lot of motion blur, and within the Motion Blur settings, you can adjust the samples up to give a smoother motion blur and/or adjust the chatter angle, to match the type of blur in the scene.
If we close that, notice there's another option for Decontaminate Edge. If we expand the view of our Effects Controls by dragging out to the right, you'll notice this doesn't just decontaminate the edge, it Decontaminates the Edge Colors. So let's go back to our Layer comp window and in the bottom, let's click on the pulldown and change the Alpha Channel from Alpha to RGB. This way we can see exactly what the edges of our image look like. If you press the Spacebar we can grab the Hand tool and click and drag.
I want you to look at this leaf over here in the lower right corner of your comp. Notice how the edges are a little jagged. If you open up the Decontamination options, we can't really increase the Decontamination Amount. If I decrease it, notice how this edge has kind of a halo around it. So we definitely want the Decontamination Amount up at 100, and if we select Extend Where Smoothed, what this will do is just make an adjustment to the areas that you've actually started to adjust.
Now in order to select Extend Where Smoothed, we need to increase the Decontamination Amount. If we move up to the right, notice, now all these stray pixels on the right-hand side have disappeared. Let me reset that back to 0 and you can see how ragged that edge is. But if we actually increase this amount, it's going to deal with the colors and make things a little bit more smooth. Since we've increased our Decontamination, if you select Extend Where Smoothed, this will adjust how the edge actually works, based on this increase setting as well as the Reduce Chatter setting.
If both of these are set to 0, there is no reason to extend it, because nothing has been smoothed. View Contamination; if you select that, now you can see the amount of area that's been decontaminated along the edge of the matte. Now there is one last thing I want you to check out. So let's deselect that last selection, and let's actually hover our mouse over the Layer comp window and press the Tilde key. That's going to maximize this in our interface. In the lower right corner there's this button called Freeze.
And basically, once you've gone through and adjusted your Roto Brush to the settings you like, you should freeze your Roto Brush selections. What this actually does is allows After Effects to apply the Roto Brush, so every time you load up a RAM preview and that kind of thing, it's not redoing the selection using the Roto Brush. This in essence is freezing the selections you've made into a pre-rendered section. So once you're finished with the Roto Brush, remember to freeze.
And if you need to come back and make adjustments to your Roto Brush, just understand you'll be prompted to unfreeze your Roto Brush selections by selecting this button. So as you can see, the process for refining the edge of your Roto Brush is just as important as actually developing the initial selection in the first place.
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