We don't always have the luxury of taking footage with a green screen.
Sometimes you may have a clip that is perfect for your project and you want to change the
background or even just color adjust the background separate from the foreground and you don't
have a green screen to be able to do that.
You can take found footage and edit it from the background in After Effects.
One way to do that is to use the Roto Brush.
Notice that the Rotobrush does not work on a Composition.
It works on the footage level.
Right now I'm viewing in a composition window, the composition.
What I need to do is have the footage appear in this window.
To do that double click on the footage.
You know that you are seeing the footage because it will say Layer rather than composition.
You will also see these masking options down here similar to the select and mask tools
of Photoshop and a timeline.
To use the Roto Brush we select it.
One thing to note that the Rotobrush can be changed in size from big to small by holding
the command or the Control key and dragging up to make it larger or down to make it smaller.
When you draw with the Roto Brush on your main content you don't want to go around the
outside edges, you want to draw through the piece, through the middle, like a skeleton.
I'm going to do that.
Now that this is selected, before I go around the edges we want to tell the Rotobrush what
is the outside of the frame.
To do that I want to hold the Option or Alt key.
That changes the Rotobrush to subtract.
You see the red there.
Now I'll drag around the outside, tell the Rotobrush that this is the outside, this is
the background.
Now we can go in and correct more of the actual figure.
We want to be as accurate as we can on this base frame.
I'll zoom in.
Remember that I can change the size of the Roto brush by holding the Command or Control
key.
Hold Option or Alt to subtract.
We can make a nice selection.
If you make a mistake like that you always want to Command-Z or Control-Z to undo.
You don't want to give the Rotobrush any false information.
Go around, make sure everything is as accurate as it possibly could be.
This will be the reference frame so we want this to be very accurate.
We can reduce the chatter a little bit, this will smooth out the Rotobrush, so we probably
want to do that.
If you look down here we have this area that has this hair, what we want to do is change
from the Rotobrush to the Refine Edge Tool.
We an draw right over the hair there and this will do a selective mask and really refine
that edge.
If you notice here we have some issues.
So we can change the view, we can switch to pink outline, we can go to mask, but if you
look in the pink outline you can clearly see that it's selecting too much.
If we go back to the Rotobrush tool and hold Option and just drag out somewhere over here,
that will remind the Rotobrush what actually is the figure and what isn't.
Now we have a much more accurate key.
We can correct this as we go along.
Once we have this base frame, notice here we have what is called a span.
We have a certain number of frames that it goes out, in this case it's going out 20 frames.
We can increase that span so it starts to calculate the entire length of this clip.
This is a short 3 second clip so we don't have to worry too much.
You could always set new base frames but we are going to use one base frame throughout
all of this.
Now we can move forward frame by frame.
Press Command right arrow to move forward.
Now we want to look around to see if there any mistakes that changed and then we say
this is fine.
We go forward one more frame and here you can see I want to fix just a little bit.
I will go ahead and Command drag down and Option.
We want to make sure that we fix everything the first frame we see an issue because the
Rotobrush propagates forward not backward.
For example, I want to fix that right there.
If it's not working you can always go i with the refine edge tool, hold option and now
it will subtract the refine edge out of that section to be more accurate.
We go Command forward.
You can quickly switch between the Refine Edge Tool and the Rotobrush Tool by pressing
Option or Alt W. Keyboard shortcuts are always going to be your friend.
Now we want to keep looking for anytime there is a mistake.
So right here I want to fix that before it gets out of wack.
We keep pressing one frame at a time forward and we see how the Rotobrush is doing.
If we see any mistakes then we go ahead and fix them.
But as you can see it is pretty intelligent and will hold based on what you have instructed
it to do.
Here we want to make sure we grab that part of the finger then we can zoom in here and
subtract that out.
Going forward.
Here is a difficult frame.
First we can easily fix this section down here.
Up here we have so much motion blur.
What we want to do is get the refine edge tool.
Just take a nice big stroke around the outside.
It will take that motion blur and do a pretty good job of only selecting it.
If we go back to the x-ray, that's all really the hand moving really quickly.
Now we can change the size of this and say really in the middle here now we don't want
you to use the refine edge and here we can say that is part of the figure.
So that's pretty good and then we can just say Option over here, this is not.
If it doesn't move you can always use the refine edge tool on subtract to just get rid
of those sections.
That gets a lot cleaner.
You still sometimes have to tell it what to do.
We'll move forward.
Now we actually want to say, no more refine edge up here because it's basically already
done so we're going to go ahead and make this all not be refined edge anymore.
So now it makes a nice selection without that.
Now we continue to go around the hand.
As you can see it does a pretty good job of tracking along as we go.
We are just looking for anytime the mask doesn't do its job.
Right here in between the fingers we can tell that this is going to be a problem area so
we can go ahead and fix that now.
You don't have to be perfect because remember this will be moving so there will be some
motion blur that you'll notice as it goes along.
Then we just quickly fix some of these sections.
We want to make sure that we get all of the thumb right there.
And check all the other sections.
Still looking pretty good.
We can smooth this out just a little bit.
Alright, so as we are going along we are doing great.
We have already gone through a whole second of footage so far.
As you can see there is some work to do but this is a lot easier than having to perfectly
keyframe out a mask.
Now we're getting great results as we go along.
Now we want to pay attention to what's happening here.
Once again we can use the Refine Edge Tool for the motion blur.
Once we do that we'll move forward a frame.
Some of this we will be able to remove.
Once again we can now subtract this refine edge from the composition.
Now it goes back to normal.
It can find the edge on its own.
Right here by the finger we can fix that very quickly.
We just keep propagating forward making sure that we fix any mistakes as we see them.
Now, once we have everything the way we want it to be, then we have to click Freeze.
So then that will freeze all the Roto brush frames that we've drawn.
That way we don't mess them up while we are editing different things.
We can always unfreeze it to make changes but that will just take more time in the rendering
and the setting up of our frames.
As you can see now the Rotobrush is going through each of those frames that we selected
and its propagating the information forward.
It will make a nice key.
We can go ahead and close the layer.
That brings us back to the composition.
As you can see now, if I go to any frame, I now have the hand keyed out.
I can duplicate this layer and on the one behind I can go to the Effects and Controls,
and I can just turn off the rotobrush.
Now if you look, I can change the opacity of the background however I wish.
I can even bring in something in between, so then we can have text that animates, we
can have it begin at the very beginning, keyframe the position and then go to the end of the
clip.
We could have the "I love the Roto Brush" move just across there.
I have a galaxy right here, I could bring this down to the bottom.
Then at the beginning of Finger Snap.
This is the one in the background, I can press T for opacity, set a keyframe here, set the
opacity at 100% and I can toggle this to a Hold keyframe, a hold keyframe will hold that
value.
Then I can go forward and as soon as the fingers, snap, so right there, right on that motion
blur snap, then I can put the opacity down to zero and it will snap right to the galaxy
and then we can be in galaxy land for a little bit.
Then we're just about to snap again, then right on that snap, I can go ahead and put
the opacity right back up to 100% and then we love the Rotobrush.
Of course we can go into the settings of our top layer and we can change lots of different
things in the Effects Control.
We can feather out and refine the edge matte.
We can smooth it just a little bit, add some feather, we can shift the edge in or out depending
on what we need to do.
And we can decontaminate the colors if there is a bright light in your scene.
Well. this is just a basic introduction to the roto brush, Hopefully you are able to
use it for certain footage that there is no way to take in front of a green screen, be
it someone you aren't in contact with or any footage that you just have in a pinch, this
is a great way to be able to do different effects and separate your footage from the
background with the roto brush tool in after effects.
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The sample video used in this exercise is available for download, the link is in the
description.
You can use it to test out the roto brush yourself.