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The After Effects Apprentice videos on lynda.com were created by Trish and Chris Meyer and are designed to be used on their own and as a companion to their book After Effects Apprentice. We are honored to host these tutorials in the lynda.com Online Training Library®.
- Understanding motion stabilization and keying
- Performing a track
- Applying tracking to effects
- Keying with KEYLIGHT
- Replacing images
- Improving the composite
- Garbage masking
- Dealing with interlaced footage
Skill Level Intermediate
I performed a successful track of these two tracking dots on my green screen set including dealing with the actor moving in front of one of those dots. What I need to do now is clean up the bad information in the track and also apply to this footage. The standard After Effects Tracker saves all this information as keyframes on the layer. So I'll press U to reveal these keyframes and there is Track Point 1, the one on the left and Track Point 2, a tricky guy in the right. As I scroll down I'll even see a gap here where it loses the plot during this track.
Now the Feature Center is what After Effects determined while I was looking around during the track. What I'm most interested in is the Attach Point, because that's what's going to be used to derive the Position, Scale, and Rotation information. I need to carefully step through here and see if there's any bad information for that Attach Point, that little plus symbol right there in the middle, and delete the bad information. So I come through here. It's holding up well, but right when this actor gets in the way you'll see the Attach Point has shifted away from where that dot is supposed to be.
I'll zoom in so you can see this in much better detail. So what I want to do is actually select and delete that bad Attach Point. Now since these are Linear keyframes After Effects will be interpolating until the next good Attach Point. So let's make sure that next Attach Point is good. I'll scroll through here until I find my dot again. It's looking so little bit on the low side, I'm going to page down, there is a good Attach Point. So I'm going to delete anything between my first good Attach Point and my next Good Attach point.
In this case, I had just these two keyframes here to delete, other times I perform this track I have had a row keyframe here in the middle. Anything that's in-between your good points, delete, get rid of them. Now when I back up After Effects will be interpolating in-between those good keyframes and give me a good attach point, even though it's behind the guy's head. Again, don't be distracted by the Feature region, because that's After Effects's search. Focus on this Attach Point and make sure that's in the middle of your tracking dot.
I'll hold Shift and press Forward Slash to fit this image back to my screen. My motion target is indeed my original piece of footage since I am stabilizing. If it was wrong I could change the other target here. Now I just need to Apply. In this shot I do want to keep both the X and Y motion and I'm also doing Rotation and Scale. I'll click OK and now I've a hopefully stabilized shot. I'm going to twirl up the Tracker and focus on these transformation keyframes it's has now created.
It's showing me Position, Scale, and Rotation, but what it's not showing me is the anchor point which is what it applied the motion to. So I'm going to hold Shift and press A to also reveal the all important anchor point keyframes. I'll queue up a RAM Preview and here is my action on the set. Actually, it holds up pretty well during the duration of this shot. But I do have a couple problems I want to clean up. Now one problem I can't clean up is right here in the middle when the camera is moving fast.
You will see these tracking dots get blurry, because the camera had motion blur during that shot. However, if I do think the Scale and Rotation are going awry, I can delete bogus keyframes like watching this dot out here, I see as I step through that on that frame is jumping out, jumping out, and tries to snap back into position. Let's look at this dot. That's a good position; bad, bad, jumps back to where it supposed to be.
So I'm going to delete these two Scale and Rotation keyframes where that dot seems to move away from where I expect it to be. That's a good keyframe, the next two are bad. I'll look at Scale and Rotation, select those keyframes, and delete. Now I have After Effects interpolate between known good information. That's another bad set there, delete those. Basically, clean up my information and make things as stable as I can during the course of this shot.
And I can continue to go through and make more adjustments if I want to. But I just want to get rid of the worse ones and show you what to look for and how to clean them up down here in the timeline. If something looks wrong, delete the keyframes, and interpolate between the good ones. The other problem I have is during the course of this shot as we change the Scale, my source shot is no longer filling the frame, and in particular is detaching itself from the bottom. So I need to move it down so the actors always appear to be in the frame.
Now one idiosyncrasy of the After Effects Tracker is that it always enables keyframing for position even though it animates anchor point instead. So I need to delete this rogue position keyframe. I'll select it, get rid of it, and instead nudge my footage down to where I want it to be at this point in time. I scrub through to make sure it doesn't jump out of frame. It looks good there. Okay, the actors are staying inside the shot for the entire duration of this shot and are now stabilized.
The problem is they have got green behind them. Well, that's what we're going to tackle in the next chapter on how to use Keylight to key out green screen or blue screen backgrounds.