VFX Techniques: Tracking Objects onto a Face
Illustration by John Hersey

Offsetting the planar surface


From:

VFX Techniques: Tracking Objects onto a Face

with Lee Lanier

Video: Offsetting the planar surface

We have our new X-spline shape following the tracking marks above and below of her eyes. This required some additional keyframing, I'll show you my solution to it. These are keyframes in all of the keyframe positions we discussed previously. I'll play it back. It's starting to follow pretty well. The tricky part of this is the perspective shift as she moves her head or turns her head. You can imagine there is a slight gap between this planar surface, which is perfectly like a piece of paper, and the dots on her cheek.

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Watch the Online Video Course VFX Techniques: Tracking Objects onto a Face
2h 42m Intermediate Jan 28, 2013

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VFX Techniques introduces common yet critical visual effects techniques that are used in film and television shows on a regular basis. This installment shows how to build complex composites with Adobe After Effects and mocha, where motion graphics are mapped to live-action footage of an actor. Author Lee Lanier starts by combining rotoscoping and effects to digitally apply makeup to an actor to disguise motion tracking marks. Then discover how to transfer footage into mocha and generate planar tracking data that you can use to motion track graphics to the moving face of the actor. Plus, learn how to build and adjust motion graphics to create the look of a virtual tattoo and a pair of holographic heads-up glasses.

Topics include:
  • Disguising tracking marks with rotoscoping and effects
  • Preparing footage for motion tracking
  • Planar motion tracking a face in mocha
  • Applying tracking data to artwork in After Effects
  • Fine-tuning motion tracking curves in After Effects
  • Animating text and graphic elements
  • Applying color and light effects
  • Batch rendering the final comp
Subject:
Video
Software:
After Effects
Author:
Lee Lanier

Offsetting the planar surface

We have our new X-spline shape following the tracking marks above and below of her eyes. This required some additional keyframing, I'll show you my solution to it. These are keyframes in all of the keyframe positions we discussed previously. I'll play it back. It's starting to follow pretty well. The tricky part of this is the perspective shift as she moves her head or turns her head. You can imagine there is a slight gap between this planar surface, which is perfectly like a piece of paper, and the dots on her cheek.

So you have to imagine what that would look like as she turns her head. So right here for example, this corner is closer to the dot than it is when she turns her head towards camera. So that'll take some experimentation. This one is working right now so we can move on and do all the planar surface. If I go to 275, that's where we started, what I can do is turn on the planar surface and see where we left off. Here is a button for that, and there it is. Previously, I simply matched the corners in my planar surface to the X-spline.

Now that's not necessary. It can actually have a different shape, like a rectangle. It'll still be associated with the X-spline but it doesn't have to match the corners. What we want anyway is a more rectangular shape to match the heads-up display we're going to add as tracked artwork. That's more in the shape of a pair of sunglasses. So what we can do now on frame 275 is reshape this. To help us out, we're going to use a new function, and that's the planar grid. Here's a shortcut button for that right here, Show Planar Grid.

What this is is a pinkish grid that shows the virtual plain that that planar surface is sitting in. Again a planar surface is like a perfectly flat piece of paper, and this is the plain that would hold it, extending in all these different directions. If I move the corners of my planar surface the grid changes also. So the grid is really useful for seeing the perspective shift but also you can use the grid lines and grid intersections as reference to line up certain features over time.

For example, if I move the corners here of the planar surface, for one, I can make it more rectangular, but two, I can line up the dots on the top of the forehead to a couple of the intersections or a couple of the corners. So here I've lined up a dot to this corner and another dot to this corner. I can use that as reference all the way through the timeline to make sure the planar surface is consistent. Doing that also places a line down the center, down the center of her nose to her lips, and that's good reference also.

Now it's more like a trapezoid right now, going off into the distance down there at the bottom. What I could do next though is straighten up the sides, more perpendicular, straight up and down, and that would be better for the heads-up display. Now for the bottom, I can use the blue edge of the planar surface as reference also. I can line it up to the top of her nose, or I should say the tip of her nose, right above the nostrils.

So once I'm done adjusting, I have some good reference features, or lines. So I have my forehead dots lined up to two corners here and here, and the center is a nice center line of the grid that goes through between her eyebrows all the way down to the center of her lips. The bottom edge of the planar surface, this blue line, is just above her nostrils. So all good reference, and of course, as I said, the sides are more straight up and down, which I can try to keep consistent throughout the timeline.

So now we have the shape for 275, and what I need to keyframe it, because this is going to slip. If I go ahead and scrub the timeline, we'll see that it tries to fall but at a certain point, it gets confused and becomes slanted. It looks like it's the slope of a mountain. All right, so what we can do is go to the AdjustTrack tab and set some keyframes to offset the planar surface. So back to 275, and go to the AdjustTrack tab and we'll see our master reference points.

The master reference points for the planar surface have the Xs in them. The Xs are just for reference so you know where you started. If I click on one of those, we'll see our first keyframe at 275. Again, those simply relates where you want the surface as how it compares to where the X-spline is, or where the corners of the X-spline are, and also where the planar surface started, in our case. So let's adjust for other keyframes. And we'll leave the grid on, again to line up various reference points like the corners compared to these dots.

So much like the X-spline, I want to look for key places where the shape slips off or starts to slide. So for example, I can go to the last frame, make sure that's good, first and last, you always probably want to do anyway. Then go deeper, say, to 240, and this corresponds to where there is the head turn. And I can just simply grab my red ends, and if I grab the red dot, so I can see that green dotted line, if I see that then I'm good because I can know I can set a keyframe there.

As I drag this like a rubber band, they will update the shape. Let me back up. Just did a Ctrl+Z there. As I move that red point and that green rubber band, you see the shapes update, planar shape updates. So what I can do is force those dots back into the corners of the grid there.

I'll continue to do this. Get the sides nice perpendicular and again, and also try to get that bottom blue line lined up with the tip of the nose, so something like that. So I can't do this all in real time, but there are some other keyframes that would be useful, for instance on frame 205. Again you can see a major slippage there. Frame 150 or 151 corresponds to that head turn. 140, 90, and the first and last frame as I mentioned previously.

So I can't demonstrate this in real time but I'll let you continue to work on the keyframes for that shape. Now it's a little indirect. Again, you have to move these red dots, get that green rubber band, and that remotely pushes the planar shape around. But if you leave the grid on, that'll make it easier to see if everything's lined up. Okay. So we used the planar grid as reference to find certain features and therefore make it easier to give our planar surface a more rectangular shape.

That's going to allow us to better fit the heads-up display we're going to eventually place in After Effects.

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