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Adjusting corner pin curves


From:

VFX Techniques: Tracking Objects onto a Face

with Lee Lanier

Video: Adjusting corner pin curves

We've successfully imported the Tracking Data from mocha, now we have a tracked piece of tattoo art. Now, it's not perfect. Remember the finger crossing over that area caused some problems with the mocha Tracking Data, so what we can do though is refine it inside of After Effects. To get started though, I'm going to pull the tattoo layer down below the finger. It needs to be below the finger. Then I want to turn off the other layers, just to save some time. So I can see through to the tracking dots, I'm going to temporarily turn down the opacity of that tattoo 50%.
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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

Adjusting corner pin curves

We've successfully imported the Tracking Data from mocha, now we have a tracked piece of tattoo art. Now, it's not perfect. Remember the finger crossing over that area caused some problems with the mocha Tracking Data, so what we can do though is refine it inside of After Effects. To get started though, I'm going to pull the tattoo layer down below the finger. It needs to be below the finger. Then I want to turn off the other layers, just to save some time. So I can see through to the tracking dots, I'm going to temporarily turn down the opacity of that tattoo 50%.

So now, I can see where it is relative to the tracking dots. Now you noticed that there is a keyframe for every frame for the position, scale, and rotation. Now the changes in scale for instance are not that great, as is the rotation, so you don't necessarily need all these keyframes. One trick to edit the resulting curves is to simplify these properties. So for example, let's have our scale. Let's look at it first inside the graph editor. Here it is, a lot of keyframes but not much change.

The few places where there's a big change are the places we actually need to edit because of the finger cross. So let's try simplifying it. What we can do is highlight Scale and open up the Smoother window, Smoother. And use this to decimate our curve. What this tool does is it simplifies a curve based on the tolerance, but tries to maintain the shape as best possible. Because there's a very little change on our scale, we can try a fairly high tolerance of three, and then apply, and that's the number of keyframes we have left when we're done.

If I look back in the Graph Editor, you can see there's just a few bends here, and again those are the areas that we have to edit anyway. We can do the same with rotation. Now one reason to do this, to simplify the curves is, we're going to need to edit the curves by hand, particularly where it's bad where the finger crosses. If we have a super dense set of keys, it's going to be very difficult to edit those areas. In any case for rotation, we can try to simplify this with a tolerance of one.

There we go, fewer keyframes, it'll be easier to edit. But again it's maintained the basic shape. So we're not losing too much information. Now while the main problem area is when the finger crosses, there's probably some slippage, a tiny bit of slippage at the beginning between frame zero and 70. It's because the resolution of those dots is so small that the tracking is not perfect. You can see it if you playback that area. I'm going to zoom in on the timeline so I'm closer to that section.

We'll frame up here and play it back. It's very subtle but there's some frames where the relationship with the tattoo to those dots shifts just slightly, like right here. Right here I can see more of the white dots. In other words, there not covered as much, whereas earlier, they were covered more. If I go back to the last keyframe, or even the first, let's go to the first keyframe, that's how they're covered.

There's a little bit of white on the upper part and to the left of the tattoo, so I can go across the current keyframes and check the quality. Looks like it slips a little bit here, and a little bit here, I see more and more of the white dots. So in this case what you can do is offset the animation by changing the rotation. It's not the scale that's really wrong, it's the rotation in this case. So you can interactively slide the value, or try to enter values by hand.

But as you do it, it rotates around that key point. It's a little hard to imagine because there's such slow resolution, but it's worth a little work in this area. Let's see what the next keyframe looks like. Pretty good, here's this keyframe, and here's the first. So you have to compare keyframes to each other and see if they're relative. But I would go ahead and examine zero to 70 and make any kind of adjustments you feel are necessary.

Unfortunately I'm not going to be able to finish all this keyframing in real time, it'll take too long. So continue to work on this on your own. So that's the first section, 0 to 70, is the first part to take a look at, then of course is the area where the finger crosses. This is roughly between frame 72, which I'll go to, where the finger just starts to cross, and frame 113. Now here's a problem with the shape warping.

If you remember in mocha, the corners were warping and it was changing size. So in this case, we can go up to the Corner Pin information and adjust that. Again, that's under the Effects, as a Corner Pin effect. So in anticipation of that, I'm going to delete some keyframes, and I don't want to simplify all these curves with the Smoother tool. I'll lose too much information, but what I can do is cut out the bad section. So if I zoom in, so I start around 72 and end at about 113.

What I can do is highlight those keyframes for all four corners and delete them out. So you might want to make sure you know which ones you're deleting first. So if you're concerned, place your time slider to make sure it's the correct location, so this is 72 here. It's where I want to start, the third column over, and then 113 is right here, so third to second to the last, highlight all of these by drawing a selection marquee and deleting them.

Now there's quite a gap there, so what you'll have to do is bisect to try to rebuild the animation in that area. So let me just start in the center. And you can move each one of these corners individually. If you click on one of the corners, like upper left, you'll get an interactive circle with a little X in it. You can move these by hand, just like this. So again, comparing to some other recent frame, like frame 71, see where the tattoo lies, just visually, for instance, this dot up here peeks through on the left.

This dot here is pretty much mostly covered. This dot over here is mostly covered with a tiny bit of white on the left, so make some visual notes and then try to replicate that position. So I can see on this frame, which is frame 92, I'm seeing much too much white to this dot, maybe a little bit too much of this. Now you have to go back and forth, but after a little massaging, you can replicate the correct position. Once you get that middle keyframe set, then you can change any of these four corners, continue to bisect.

I go in the center again. I definitely see it slipped off here where I'm more on the left side of the dots as opposed to the right. And then bisect over here, and so on and so forth. Now you're not necessarily going to need a keyframe on every frame in this gap, but you do have to continue until there's enough for the shape to follow and not drastically slip off. Once again I'm not going to have time to complete this during this video, so continue to work on this section and keyframe it until that tattoo stays where it should be where the dots are.

We've taken our tracking data from mocha to determine where it wasn't quite working and then massaged it by editing keyframes. With the transforms like Scale and Rotation, in anticipation, we use a smoother tool to try to simplify it. And it helps us place new keyframes without having such high density in that area. In terms of the Corner Pin, we just deleted out the bad section and started to bisect. So this might be a little tedious, but this is a good way to improve the most tracking data.

You rarely have data that's perfect, so it's good to know how to go into the transforms with the Graph Editor and make some changes.

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