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Dealing with obscuration

From: After Effects Apprentice 12: Tracking and Keying

Video: Dealing with obscuration

I've chosen which two dots to track with my two track points to stabilize Position, Rotation, and Scale, but I have a problem where one of actors walks in front of one of those dots. So I need to be careful with how it set up the After Effects options as well as the search region around this second track point. First, I'll go into the Options dialog. I always need to look at Channel. In this case, I've light green versus dark green. So Luminance is my best choice. I've removed any fields or pull down from this footage.

Dealing with obscuration

I've chosen which two dots to track with my two track points to stabilize Position, Rotation, and Scale, but I have a problem where one of actors walks in front of one of those dots. So I need to be careful with how it set up the After Effects options as well as the search region around this second track point. First, I'll go into the Options dialog. I always need to look at Channel. In this case, I've light green versus dark green. So Luminance is my best choice. I've removed any fields or pull down from this footage.

No need to Track Fields, always leave Subpixel Positioning on. Since the back of this green screen was towards the back of the stage and therefore out of focus, he starts a little bit on the fuzzy side. If you've trouble getting a good track, you might want to try Process Before Match and Enhance or sharpen the footage, but I can leave that off for starters. The real important thing is how to set up these parameters down here. I don't need to Adapt the Feature On Every Frame, because it's keeping pretty much the same shape and isn't really changing size that much. But what's really important is this pop-up.

What happens If my Confidence goes Below 80%? Well, when the actor goes in front of that dot, I'll pretty much will lose the track and lose therefore any Confidence that I founded. I don't want to Continue Tracking, because I've lost the shot. I don't want to Stop Tracking. I need to figure out a way to get around this. What I want to do is Extrapolate the Motion. Tell After Effects, okay, I know you can't find the dot right now, but keep going in the same direction at the same speed you were before and let's hope that it reappears. So I'm going to choose this option. I'll click OK.

The next very important thing is what is the size of this search region? If it's too big or too small you'll have problems. And let me demonstrate. I'm going to start off by placing it very large, because I'm saying, you know, this actor does walk in front of this dot, let's give a larger search region so that After Effects has a better chance of finding the dot afterwards. This sounds like a solid idea. I'm starting at the very beginning of the clip, I'm tracking forward, and watch what happens to this track point. It's initially good, because it's not obscured.

Here comes the actor though. You see the actor pushes it out of the way and it never finds the dot again. That didn't work at all. So I'll undo and let's try again. Let's go to the opposite extreme. Let's make a very tight search region so you don't go looking off into space of this dot, but stay more tightly focused on where you need to search. I'll click Analyze forward again, you will see it's much faster with a small search region. It found the dot, but it loses it again. What's going on here? Well, the small search region helped After Effects extrapolate back and find that dot.

However, the camera is moving so violently that in some of these subsequent frames like right around there, the dot has moved so far, it's gone outside of my now smaller search region, and that's where we lose the track. That doesn't work either. I need a compromise where my search region isn't so big that I completely lose the track, but isn't so small that I lose it just because the camera movement. I'm going to undo. Since I notice my problem was with the dot going off in this direction, I can go ahead and hold the Command key on Mac or Ctrl key on Windows and pull out these dots just in the direction of movement, saying here is where my motion is, worry about that, I can stay tight on this side.

Now let's Analyze forward. It's still finding the dot, the actor comes in, found the dot again, and now during the violent camera movement we continue to find the dot. We kept an accurate track. This is the most graphic example of where you really need to coordinate your track points with your options to get a good track. Just to hammer that home I'm going to undo for a second, go to my Options, and say I decided it might be a good idea to Adapt the Feature On Every Frame since the camera is moving. If I perform the track again you'll see that After Effects again has trouble finding this particular dot.

Since After Effects was making microscopic changes from frame to frame, because it was adapting the feature in every frame, it couldn't refind that original shape. So I want to emphasize; you will not have success your first time out motion tracking unless you're very lucky or very good. You'll need to play with different parameter settings and different track points until you do get a good track. Let's go ahead and get that track now. I'm going to scrub through to verify that I've indeed followed those dots, and I'm fairly happy with that track.

I do have a little bit area right in here where I'm lost in the wilderness. So in the next movie we're going to focus on cleaning up these problems and also applying the stabilization to the original footage.

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Image for After Effects Apprentice 12: Tracking and Keying
After Effects Apprentice 12: Tracking and Keying

39 video lessons · 14082 viewers

Chris Meyer and Trish Meyer
Author

 
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  1. 9m 2s
    1. Welcome
      2m 38s
    2. The Tracker panel
      4m 24s
    3. Using the exercise files
      2m 0s
  2. 13m 25s
    1. Warp Stabilizer basics
      5m 59s
    2. Warp Stabilizer advanced parameters
      7m 26s
  3. 30m 6s
    1. Setting up a stabilization
      2m 57s
    2. Track points explained
      5m 48s
    3. Performing a track
      5m 11s
    4. Applying a stabilization
      2m 42s
    5. Cleaning up the results of a stabilization
      3m 0s
    6. Performing a motion track
      5m 57s
    7. Applying the results
      4m 31s
  4. 13m 48s
    1. The Radio Waves effect
      4m 16s
    2. Tracking the mountain
      5m 31s
    3. Compositing the effect
      4m 1s
  5. 24m 28s
    1. Perspective tracking overview
      2m 40s
    2. Tracking to a corner pin
      7m 1s
    3. Improving the composite
      5m 39s
    4. Tracking with mocha-AE
      9m 8s
  6. 31m 49s
    1. Tracking in 3D (new in CS6)
      4m 31s
    2. Creating 3D objects (new in CS6)
      5m 12s
    3. Hanging a poster (new in CS6)
      8m 8s
    4. Adding text (new in CS6)
      5m 33s
    5. Using shadow catchers (new in CS6)
      8m 25s
  7. 16m 46s
    1. Tracking dots
      5m 43s
    2. Dealing with obscuration
      5m 12s
    3. Cleaning up the stabilization
      5m 51s
  8. 12m 40s
    1. Basic keying
      7m 20s
    2. Refining the key
      5m 20s
  9. 13m 32s
    1. Quizzler challenges
      3m 35s
    2. Quizzler #1 solution: Stabilization plus masking
      2m 58s
    3. Quizzler #2 solution: Stabilization plus tracking
      2m 50s
    4. Quizzler #3 solution: Copying a camera's motion
      4m 9s
  10. 12m 28s
    1. Tracking for multiple effect points
      4m 44s
    2. Converting to ray-traced 3D (new in CS6)
      7m 44s
  11. 23m 59s
    1. Legacy tracker advice
      8m 14s
    2. Tracking interlaced sources
      5m 59s
    3. Using garbage masks for keying
      4m 51s
    4. Using the Rolling Shutter Repair feature (new in CS6)
      4m 55s

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