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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're ready to move on to Project 4. In Project 4 we're going to apply motion tracking in a different form. It's going to be Corner Pin tracking. Corner Pin Motion tracking is great whenever you have to track a rectangular or a square feature. For example, you might track the corners of a billboard or a poster or a window or a screen, anything that's rectangular. After you track, you can then apply new artwork or new footage to that rectangular area. In fact, in Project 4 we're going to replace the screen of a futuristic PDA device, so let's get started.
Let me go to File > Import > File and pull in that original footage, features an actress. This is called shot4 in the Footage folder, so I'll bring that in as an image sequence. I am going to pull that down into the timeline and create a new composition. Let's play it back and see what it looks like. So you see this features a PDA, has a screen, that screen is blank. We're going to put in new artwork in there, in fact, we have an animation that was pre-done we will put in this area. So we are going to Corner Pin track this green rectangle, let's get started. So you start the same way, you pick the layer and go to Animation > Track Motion.
Now tracker opens up in Transform mode, once again, so you can switch that. Now there are two types of corner pin, there is Parallel corner pin and Perspective corner pin. We actually want Perspective corner pin because that give us the ability to move all four track points that we will have. And in fact, once I choose that there are the four track points, if I zoom in, you see 1, 2, 3, and 4, and these are all attached by strings, but you can move anyone of them separate from the others. So the idea is to place this at the corners. So I'm going to go to frame 10, it's a good starting place, not much motion blur, and place these track points.
So you want the corner at the very edge of the corner where the green meets the blue. So now that these are positioned, we can try to analyze. So I'm going to analyze forward, you can see as it analyzes, it looks like its pretty stable. Let's try 10 to the start. Okay, it definitely slips off here. You see the actress lifts up her hand to raise up the PDA, so there's some amount of motion and blur, and the tracking is just not able to figure out where are those blurred corners are. They are almost invisible now because there's so much blur.
We could try to adjust the track points further, change their sizes and reanalyze, or you can just manually adjust it. Let's see how many frames are bad in this case, so look pretty good around frame 6 or so, so the first 5 frames are starting to slip off. What I'm going to do is manually adjust this. I'm going to do at on frame 5 first, it's not too bad, so I'm going to zoom in, because what you don't want to do is accidentally select any of the keyframes on motion paths, so you have to look pretty closely. So I'm going to fix track point one, two, let's get down to three here, and then four.
I do have to do the other frames. I'm going to skip ahead though, because that might take a little bit time to move all four of these track points. So we have now jumped ahead, I have adjusted frames 1 through 5 or so, and now I'm ready to deal with frame 0. Frame 0 has a biggest slippage, you can see how far off it is. I'm going to try to adjust the track points for this frame. Now here I have accidentally grabbed one of the keyframes from the motion path, you can see it pulls out there is a little square box here. I want to undo that. Ctrl+Z, or Command+Z, so if you have a hard time selecting the anchor point without getting one of the motion path keyframes just zoom in, and then it's easier to select.
So you fix frame 0, so now 0 to 5 or 6 is correct, so now if I move forward, you can see that the track points follow that square, the rectangle. Now we're ready to try to apply this, now the application happens a little bit differently, I do want to apply it to different layer, but I want to prep that layer in advance. So with this project there are some premade animation that features some screen graphics, let's bring that in. File > Import > File, it's in the Renders folder, it's called Shot4Screen, bring that in, we're going to drop that on top of the composite.
Now I do need to prepare it for apply the motion tracking to it. Now because the corner pin will apply the tracking data based on track point one to the upper left-hand corner, it's actually a good idea to zero out the anchor point which is right here and the position of this artwork or whatever you're going to play the tracking data to, so it sits in the upper left-hand corner, and just do that. I'm going to expand the transform section of this new layer and zero out the Anchor Points 0,0, and also the Position. You'll see that it stuffs it into the upper left-hand corner. This is actually the idea for the corner pin tracking though.
So I can go back to the tracker, make sure I check my edit target, make sure my screen is selected in terms of this new layer, click OK, and hit Apply. As soon as I hit Apply it snaps that artwork right to the screen. If you look at the layer you can also see that it's had a corner pin effect, and that's where it stores the position of the four corners terms X, Y for upper-left, upper-right, or left or right. In other words, all four corners of that artwork are pulled down to these positions.
It's also animated the overall position of the entire layer. Let's play it back, so it's looks pretty good. There are so some issues with some of the early frames, because of the heavy motion blur, doesn't quite match exactly. There's also little bit of wiggle in there. Now we can deal with that, and we'll talk about that a little bit later. We have the basic tracking down now. So now we can move on to better integration of that animation with the background.