Join Lee Lanier for an in-depth discussion in this video Rotoscoping greenscreen, part of VFX Techniques: Crowd Replication with After Effects.
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We've assembled a nice front row crowd here, we've also adjusted the background quite a bit. We're now ready to move on to the second row of the crowd. So, many of the same issues will apply in terms of green screen but there will be some new problems that crop up. Let's get started. I'm going to go and get the 2A Crowd File under Footage/Crowd 2A, we'll drop that on top and talk about it. Now it looks the same except at the very end, this actor is so tall, his hands crossed over the edge of the green screen, that's bad.
That means we can't do a simple Garbage Mask but we have to Rotoscope that to save his hand, if we don't, we either cut off his hand, we wind up showing all this garbage up here. So, we start the same way, by drawing a Mask, but I will take in to account his hand shape. So back to the Pen tool, I'll draw a Mask, and I will start a very simple, and I'll add to it.
Now just so, two things more clearly, I am going to turn on my test background once again, I can turn off my other layers if I don't need. So, first thing you need to do is to take into account his hands so one way to do that would be to insert additional points here. You can either go to the Add Vertex tool or just let your mouse hover over the masked line. I going to add a few more points here and then I could shape those.
This is a good frame to start on because his hands were crossing over the bar just barely. Now if you have enough points, add some more, now if his hands are crossing, not to worry about them. They do cross over at some point, so it's that one more point right here, give that a try, there is a good frame. Now this will definitely be keyframed over time. So I am going to activate the Time Icon for the Mask Shape and then move on to another frame.
Now one way to approach the Rotoscoping is to set a key where there is an extreme position. For instance, as his hands are wide open and/or when his hands are touching each other. So you might want to just play the timeline, figure out where those key positions are. For example, right here. I want to reshape the mask to fit this new hand position. Now it's just going to take some time, so I am going to skip ahead and show you the final result in a few seconds. Now, I do want to also mention the fact that there's a problem down here with this concrete patch showing through, we can't green screen that out.
What I can do, though, is create a second Mask to subtract from that area. So I am going to grab the Pen tool one more time and draw a Mask over the top here that fits that kind of triangular shape up to her calf. I don't want to add this one, I want to subtract, so I' going to set that Mask 2 menu to Subtract. This will also be animated over time, so I'll go ahead and turn on the Mask Path keyframe, that sets the key and then we go to some other frame and then reposition it.
So, both of these masks will have to be keyframes. One to remove this concrete patch and two, to make sure his hand stay in frame the entire time, without revealing any of the other garbage. So now that I had the basic Masks drawn, we're ready to construct the rest of the crowd. We'll be taken somewhere steps by applying garbage masks, the green screen tools like Keylights and then Transform Tracking. Now there will be some additional Rotoscoping, for example, on 2B, the actor's hands crossed the edge of the frame once again so that requires some additional work.
But since many of the steps we have done before, I'm going to skip ahead and show you the end result. Remember, keyframes now in both Masks is quite a few on the Mask 1 that's taken care of the garbage mask and his hands, and if you are on the Mask 2, that's taken care of this concrete patch right here. If I play it back, you'll see the Rotoscope follows his hands at the top. So, now it's ready to go through the green screen process and have that removed. The same time, I am going to go back into the PreComp from 1A to 1D, go to 1D, select that and steal its effects.
So I'll just copy the Keylight, the Channel Blur and the Curves and go back to the Add Crowd Comp and paste those on to 2A. Anytime you do that, you should probably adjust the settings, you don't want to just leave it as it is if you turn back on the background, see it looks pretty good, but I still would want to go into Keylights, and adjust things like the Clip White and Clip Black, make sure that's good, some of the other settings.
Also any other effects you might have, like in this case, there is a Curves for the Alpha which erodes the edge, that's looking pretty good. Now we're ready to Motion Track this. Now because this is a separate row, it's further back, I will make a brand-new tracker, so I'm going to pick the lowest layer, go to Animation > Track Motion. Now this is actually Tracker 2, even though we pre-rendered out this lowest layer here, the old tracker was carried over. So this is Tracker 2.
I do want 2 Track Points on Tracker 2 to Track Point 1 and 2, I want to put the Track Point 1 on the left, let's try the fourth X up-- or the fourth X down I guess--makes the boxes bigger and then try to go across from that and actually the fourth set of X's up, lines up pretty well over here. So I'll put Track Point 2 at that spot, here we go.
Now I'm not quite at the end of the timeline but what I can do is analyze forward, then go backwards. All right, there is a motion path, now before I'll apply that, I need to make sure that 2A has its anchor point in good position. So, there is a fourth X right there, I'll get the Pan Behind tool and move the anchor point over. Here it goes, now I can apply back to the tracker, make sure Tracker 2 is selected, the target, 2A so I am good there, hit Apply X and Y, and there we go.
Now here is a situation where there is a huge rotation -356 degrees, that happens on occasion based on positions of the Track Points. I am going to try to fix that, though. Let's see what the differences is between the first frame and last frame, so 356.3 356.6. So 0.3 degrees difference, so a large negative number. What we can do instead is get rid of this Rotation Animation, go to frame 1, and put it back to zero.
Go ahead and key that, go to the end, and then change it by the 0.3 degrees, rather negative 0.3. Now it's still the final location of screen but we can use our anchor point to get it back to where we want it. These Rotations corrected now. So I am going to slide this back up to around that fourth X that we have, and line up somebody's foot to one of these X's just for reference.
Maybe this guy's flip-flopped to this X right here, I'll go ahead and key that on the last frame now. Now go to the first frame and make sure it's roughly in the same position. Now here is a case where the Motion Path is covering up that marker, so we are going to have to zoom in really close. This is going to take some time. So I am going to skip ahead and show you the final result in a few seconds.
So, I've added Crowd 2B and went through the whole process of adding the Garbage Mask, removing the green screen, and also applying the Motion Tracking. Here's the mask, it's not animated, so pretty simple shape, the green screen tools are similar, it's combination of Keylight, Channel Blur, and Curves once again. For Motion Tracking, I just parented 2B directly to 2A, and once again, animated the anchor point to make sure that some marker lined up with the people.
For example, I have this woman's heel right in the corner of this blue tape mark. So, 2B is done, now we're ready to move on to the third part of this row which is 2C, and that will require some additional tools we have not used yet.
- Setting up your project
- Removing camera jitter
- Motion tracking CG renders
- Creating light effects
- Keying with Keylight
- Solving bad matte edges
- Rotoscoping green screen footage
- Color grading to match elements
- Relighting the scene