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Explore how to use the motion tracker and stabilizer built into After Effects and shows how to handle a variety of shots. Author Chris Meyer leads a quick tour of the third-party software mocha and demonstrates the workflow for The Foundry's KEYLIGHT, both bundled with After Effects. The course also covers tracking a greenscreen shot with a handheld camera and replacing its background.
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®.
In this chapter, we're going to take on a far more challenging stabilization and in the next chapter, we'll show you how to do some green screen keying. I've already done, Close All to close my previous compositions and if you have access to the exercise files, open up 05-Keying*starter. This, by the way, is a high definition shot, 1920x1080, work in Square Pixels, in a common filmic Frame Rate of 23.976. However, as a side note, if I go look at this source shot in the Project panel, you know that its source size is 1440x1080.
This is a common so-called anamorphic format the high-def video captures, and if I go into the Interpret Footage dialog, you'll see that I've set this Pixel Aspect Ratio for HDV 1080 with a ratio of 1.33 to 1. That means this original shot needs to be stretched out horizontally an additional 33% for to look right. If you're new to the subject of non- square pixels, go check one of the sidebars at the end of our fourth Apprentice course on layer control where we give you a quick primer. I click OK for now. Our goal is to take this shot and place it over a brand-new background.
Now you can tell from this green screen with these lighter green tracking dots in the background that this was a handheld camera that follow the actors on to this set. Fortunately, they had the foresight of putting these light green dots here to give us some reference against an otherwise featureless green background. We want to put these actors over this still image of a new background of an inside of an old abandoned barn. Unfortunately, this is still; it's not moving. So what we need to do is stabilize this shot so the actor is have the right movement and perspective in relationship to the background we want to place them over.
By now you know to track or stabilize any shots, you need to double-click it to open it up in its Layer panel and here is where you see this so-called anamorphic squeeze of this shot. It's actually been captured skinnier than it is in real-life. That throws you off, you can go ahead and use this little button, Pixel Aspect Ratio Correction, to see it as the way you want to displayed in your final composition. But personally, when I'm working on sources, I like to see the original pixels, nothing artificially stretched for display purposes, so I know precisely what it is I'm working with.
Okay, I need to stabilize this shot. If you have After Effects CS5 or earlier, you would normally just click on this Stabilize Motion button. If you've After Effects CS5.5 though, clicking to Stabilize Motion button would invoke the new warp stabilizer. It just so happens the warp stabilizer has troubles with a shot, because the principal motion in the shot are the actors. However, they are not who we want to stabilize. We want to stabilize the dots in the background. If you watch our course, After Effects CS5.5: New Creative Techniques, I devote a whole chapter to the warp stabilizer as well as a movie of how to deal with this shot using warp stabilizer.
But in this case, we're going to use their traditional After Effects stabilizer. Since I am running 5.5, in this case, I need to click Track Motion, then select the Track Type to stabilize. Again, if you're using an earlier version, you just click Stabilize Motion. Now in the case of this shot not only is the position moving, you'll notice that also the camera is pushing in so I have a scale difference during the course of this shot; there is also some slight rotation to the camera. So I need to stabilize three parameters; Position, Scale, and Rotation, not just position.
No problem, Position is on my default and I just add Rotation and Scale. That gives me two track points, because After Effects needs to measure the distance and angle between these points to decide where are the changes in scale and rotation. Next comes picking which dots to track. What I need are dots that is far away as possible because the more distance I have the more accurate the measurement of scale and rotation, but also dots that are visible for as much of the scene as possible.
And so I scrub through this, I see that the two dots on the right go off-screen at the end so I can't really use those. This dot down in the lower left is initially blocked by the actor so that throws that out. I'll be working what this dot looks like. Now let's look at these three. These two are further away over here as I scrub through, the actor in the blue shirt walks in front of both of them, but blocks the lower dot more of the time. So I think I'm going to end up using these two dots.
I'm going to zoom in so I can see things in better detail; quickly position my Track Points over these dots. I need a little bit of widening here to go ahead and capture that entire dot, a little bit more margin that will help, and increase the search regions since this camera does move quite a bit in the shot. And now let's move this one to the track point over to this dot. Again, make it wider to capture an entire white dot surrounded comfortably by the dark green background and set up a search region around this.
Setting up this search region properly is vital, especially since the actor walks in front of it during the course of the shot. So in the next movie, we're going to focus on how to set up the search region as well as the tracker options to best deal with this obscuration problem.
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