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- Working with image sequences
- Matching the 3D camera to video footage
- Lighting models in Maya
- Splitting a scene into multiple render passes
- Batch rendering
- Recombining render passes in an After Effects composition
- Setting up motion trackers
- Refining layers with rotoscoping
- Adding blur and effects
- Adjusting shadows and matte edges
- Using color correction
- Stabilizing shaky video
Skill Level Intermediate
We placed the spaceship layer over the background footage. Now we're ready to try to motion track the ship so it matches the camera movement of that footage. Let's take a look at it. One thing you'll notice is that there is more chaotic motion, particularly at the beginning, also the fact of the camera's rotating or tilting left and right. If you watch the top of the building, you can see how that perspective changes quite a bit. That tells us two things. One, we need to have the tracker figure out the rotation of the camera. Two, the fact that there is lot of chaotic motion at the beginning of the footage, means that you probably want to do the tracking from the end of the timeline towards the beginning, in terms of analyzation.
When we go to the last frame, let's apply a tracker. I'm going to pick shot2, go to Animation, and apply Track Motion. Now in order to have it to figure out the rotation, I need to select the Rotation check box right here, Position is turned on automatically, in this case I need Rotation also. When you click on Rotation, you get a second track point, that's necessary to figure out how the camera is tilting, so track point 1 and 2. The idea is you place these over two separate features. Let's take a look, I'll zoom back.
We are fortunate in the fact that there are two lights in the side of the building that are good candidates for this. I'll place track point 1 on the left one and track point 2 on the right one. So I'll zoom in and just click-drag these by the empty portion of the center to reposition them, so track point 2 will go over this light here. Now the track point boxes are smaller then the light feature, so I am going to expand this box--just want them to encompass that feature loosely. So here is track point 2, now track point 1, there we go. Let's try to analyze this from the end of the timeline backwards.
All right, let's take a look at track point 2, that's looking pretty good, now track point 1. It's here already on frame 0, it slipped off, and however, the rest of the motion path looks pretty solid, so you could go in and adjust the track points to continue to reanalyze or check the options in the tracker. In this case, though, because I only have maybe two frames that are incorrect, I think I'll manually place the track point. So on frame 0, I'll drag it back up to where it needs to be, and in frame 1, do the same. All right, that's looking pretty good. So now we have motion paths for these two track points, we can apply it to the spaceship.
Now there is a potential issue. Normally when you apply the tracker to a layer, it keyframes the properties. In this case, because we have Position and Rotation, if I apply to spaceship, it's going to animate position/rotation here. Therefore, although I can offset the positions to the anchor point, I cannot offset the rotation unless I change the resulting keyframes. That could be a lot of work. So one thing we could do to avoid this potential problem is apply the tracker to a Null and then parent the ship to the Null.
Now what's a Null? A Null is a special layer inside After Effects, it doesn't actually render. It has a set of Transforms which you can apply something like a tracker to and parent things to but doesn't occlude anything below it. So if I apply the tracker to a Null, then parent the ships to the Null, I'm free to later adjust the position offset or rotation offset on the ship layer itself. Let's try that. Now there is one thing we should probably do before we apply it though to the Null, and that is remember that the tracker applies the data based on where the anchor point is for the layer, so the anchor point is basically stuck to the motion path.
Now in this case, because we have two track points, that'll be stuck to the motion path for track point 1. So we really want the anchor points for the Null on the spaceship over here where the track point 1 is. Let's go back to the composition view. So here is the spaceship. While we have that, let's go and select that layer and move it to anchor point from here, down to where the light is for frame 0. Let me go to frame 0. I want to use Pan Behind tool to move that, and I'll zoom in so I can see it better. So there is pretty much the center of that track point 1 for that frame, frame 0.
Okay, so we need a Null. I have already created a Null inside After Effects, you go to layer > New > Null Object, and there is a Null, it comes in as a red bar, it's indicated by red square inside the viewer. Now this doesn't actually interfere with the final render, it's just there for reference. It also has its own anchor point at the top left, and that's red. So while we had a Pan Behind tool activated, let's try that over also, I want to put in the same place, about right here. By doing that when we apply the data, it's going to make that the ship is pretty much where it needs to be right here.
Okay, I'm going to go back to the Selection tool. Now there is one another step we should take, we fix the anchor point for the Null, fix it for the spaceship, but we have to think about what to do with the matte. Remember the mattes supplying the Alpha to the ship, so it needs to travel also, so I'm going to do that through parenting. I'm going to parent the map layer to the ship and then make the ship follow the Null. I am going to parent the ship to the Null, so matte is parented to the ship, the ship is parented to the Null. So now we're ready, fix the anchor point to care the parenting, we have the Null, now we can apply the data.
Now we go back to Shot2 and make sure I can see the motion tracking, click the Edit Target, select the Null, click OK, then apply the data, Apply, and Yes for X and Y. So here the Null has picked up the motion tracking data, and therefore the ship is following the Null and the matte is following the ship. Now there is a problem. You see how it's rotated? Looks like it's a little off kilter there. Let's play it back until it's going on. So the ship feels like it has the same motion as the camera, so the motion tracking is therefore successful.
However, it's off a bit in terms of rotation, but since we use the Null, we can offset that. Now the Null itself has the position/ rotation animation placed on it by the tracker. Now if I go down to the spaceship layer, you can see the position/rotation are still free. So what we can do is change the rotation--offset the rotation and get the ship back where it needs. In fact, if you enter 7.5 into the Rotation, it snaps back down to where it needs to roughly be, on top of the building. Now it's not exact match yet. We left those planes we placed in Maya little bit loose, so our layer step will deal with a really tight fit, but at least the ship is rotated correctly now.
We'll play it back, rotation is now correct. Beside from the edge tightness here, eventually there is the issue of the fact to seeing cut off here, but we'll deal with that in the later step. So we have successfully motion tracked this footage through two track points with rotation and position and applied that to a Null, and the Null basically drives the ship and the matte layer along.