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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.
I've completed the keyframing for my X-Spline shape. If I click on one of the X-Spline points, I can see the keyframes here on the timeline and each one of the corners has the same keyframes. Let's play it back. And there you go. All right, that looks pretty good. It's following fairly well, except where the finger crosses over the shape.
We're going to have to deal with that separately. In fact, we'll need to edit that in After Effects. Unfortunately, that's a very difficult thing to track automatically. Now we could add additional keyframes here, but too many keyframes too close together makes for a bad set of motion tracking data. It's actually easier to edit small areas like this, in this problem area, inside After Effects. Now there's other work we can do though, and it has to do with the surface, the planar surface. Remember we corrected the surface or placed the surface on Frame 200, so it fits the shape.
Let's see what happens on the other frames. As I scroll through, it gets confused about the appropriate location. It tries to make the planar shape relative to the X-Spline, but the program doesn't quite know how to do it the entire time. What we can do is go to the AdjustTrack tab and offset that planar surface, so it gets forced into the correct position. This is like a different set of keyframes just for the planar surface.
It's important to get the correct shape because we don't want our tracked artwork eventually to grow and shrink inappropriately. Before I go to the AdjustTrack tab, I want to briefly mention a few things about the Track panel. Now we're using most of this in a default state and that's actually fine. For example, there's a Motion section that determines what you're tracking. Now this is similar to After Effects where you can track Translation and also Rotation, for example. In this case it's Translation, Scale, Rotation, and Shear by default. There is an option to turn on Perspective, but in this case we'd get better results with the default.
There's also an option for what you're tracking in terms of channels. We're tracking Luminance, which is fine. Even though we adjusted the Hue and Saturation and the Brightness of our image sequence, we increased the Contrast because increasing the saturation increases the contrast between channels. So this works fine here. And Luminance is simply brightness of the image. There's also the ability to track different styles in motion in terms of big movement or small movement. In this case, large motion works well for us. In any case, let's go back to the AdjustTrack tab and we can adjust this surface.
I'll zoom in, and if I'm on Frame 200, there'll be big Xs. In fact, before you go to the AdjustTrack tab, I would suggest going to Frame 200 first and then go to this tab. The idea is to have these master reference points on Frame 200 where the shape is appropriate, where the planar surface fits correctly. These don't affect the quality of the tracking, they're just reference to say that's the first frame where you placed the surface.
We can click on these points here and you get these big boxes around them, they're green and pinkish. You can move these, and every time you move these it gets a new keyframe set for the planar surface for each corner. Now since I placed that surface on Frame 200 that's where I get a key. What I can do now is go to other keyframes where there is slippage of that shape, like Frame 0, and move that planar surface to get it back to where I want it.
So what happens is when you click on one of the corners there, one of those red boxes, you get a green dotted line. You can move it to where you want it. That will be the new position of that corner, and you let go of the blue surface updates. You have to be careful. You might have to zoom in really close. I'm just going to do it for a second, because you don't want to grab the wrong thing. You really want to grab the little red boxes.
And then you get that green rubber band dotted line, which represents new edges, basically. So I'm going to put them back at the corners of my X-Spline. Each one will get its own keyframe, and that keyframe will appear on the timeline. So once I move the four corners, now my planar surface is correct. It's in the correct place. I wanted to continue to do this across the timeline at critical points. This will be similar to placing keyframes for the X-Spline, pretty much where there's a big shift in motion or suddenly the planar surface slips.
So what we can do is use some of the same keyframes as we did previously. On Frame 40, we could reshape it to keyframe it, on Frame 70, 77, 88, 103, and 114, the key at those frames, then by the end of it, the planar surface will follow just as well as the X-Spline.
We've adjusted the planar surface to make sure it falls at X-Spline. And that is very important, because eventually the corners of the planar surface determines where the corners of the tracked artwork go within After Effects. So in order to avoid fluctuations in scale or strange rotations, is a very important step. We've adjusted our planar surface to make sure it fits throughout the timeline. We did this by going to the AdjustTrack tab and setting more keys in the corners. Now this is an important step, because the planar surface should really fit that feature on the face, because eventually that planar surface, at least where its corners are, will determine where the corners of the tracked artwork are in After Effects.
So you can imagine that where the planar surface is, that's where our tattoo will eventually go.
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