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Adjusting tracker options for better results

From: Maya Rendering for After Effects Composites

Video: Adjusting tracker options for better results

So far with project 1 in After Effects, we have applied the Tracker and created a successful motion path. Now, remember that the first few frames were giving us problems because of the heavy motion blur. To fix that, we manually adjusted the position of the Track Points to improve that location of the Track Point where it is compared to that feature we're tracking, which is the X on the piece of tape. Now, there are some options you can apply. There's Options button on the Tracker itself that you can adjust. Also the option to interactively change the shape of the Track Point, and we haven't talk about this yet, but there are two boxes on the Track Point.

Adjusting tracker options for better results

So far with project 1 in After Effects, we have applied the Tracker and created a successful motion path. Now, remember that the first few frames were giving us problems because of the heavy motion blur. To fix that, we manually adjusted the position of the Track Points to improve that location of the Track Point where it is compared to that feature we're tracking, which is the X on the piece of tape. Now, there are some options you can apply. There's Options button on the Tracker itself that you can adjust. Also the option to interactively change the shape of the Track Point, and we haven't talk about this yet, but there are two boxes on the Track Point.

The inner box is the feature box. That represents the region that contains the pattern that it's trying to track over time. And generally, you leave that about the size of that pattern like the X. The outer box is a search region, and that's a region that it goes into if it has a hard time finding the pattern. The pattern might be obscure because of motion blur, like it is here, or because there is erratic motion, and all of a sudden it loses where the feature is. So it will go into the search region to try to find it again. So one thing you can try to improve the motion path is just to resize these boxes.

You can click on the corners, interactively drag them to scale them in the left, right, or up, down, or both directions, and also do that with the search box too. So, what we can do is try to go to frame 10, where it's a pretty good track, and then experiment by resizing these boxes. So let's say I make the boxes really big. Now sometimes a really large set of boxes, on the Track Point, will help you track something that's a little too blurry, or too erratic. And in general, a larger set of boxes will mean that the tracking tool works a little bit more slowly.

Let's give it a try and see if it helps us. I'm going to analyze backwards from frame 10. In that case, my boxes were so large, it got completely confused, and slipped off. So, for this particular project, that's probably not a good solution. But keep in mind that sometimes it is necessary to adjust these. Again, in general, you want to make the feature box just slightly larger than that thing you are trying to track, like this X. The search box can be just made a little bit bigger, something like this is generally fine.

So let's try it again. Looking pretty good, it's still going to slip off in the first two frames. Let's talk about some of the other options though that come with the Tracker tool itself. If I click the Options button, this window comes up. It's divided into several regions. You have your Channel section, you have your Process Before Match, and then your Adapt Feature menu along with the Confidence amount. What the Channel does is allows you to track different channel elements. It sets a luminance, by default, which means it looks at the pixels in terms of their brightness, not their color just the brightness, and often this is very good.

There is also RGB where you can track based on red and green and blue values, and that's it, no brightness. There is also Saturation where you track simply by the amount of any of the primary colors. In this particular case, these channel themes will not make a huge difference, but it's good to be aware that they're there. Now, there is also Process Before Match. This will put a pre-process on your footage to help the Tracker figure out where the pattern is. I'm going to turn this on. There's Blur, and that's going to blur the image in advance, and this is good for any kind of footage that's very grainy where you have a grain pattern interfering with your tracking.

Let's give that a try, and see if that helps. I'm going to click OK and then go to frame 10 again and analyze backwards. Slightly different result, often you get a very slight difference in the motion path. Now, in this case, it didn't help us a lot because we don't really need to blur this. Let's go back to the Options. The opposite is Enhance, which sharpens beforehand. It's looking pretty good until the very last frame where it goes off of the tangent. So, in this case, I think turning Process Before Match off is going to be just fine. Now, in terms of this lower menu Adapt Feature and the Confidence, that allows Tracker to go into different modes where it reacts differently based on how successful it is.

Now Adapt Feature, what that does is instead of looking at the pattern on frame 1, it actually looks at the pattern at the prior frame. So, if you're on frame 10, it double-checks frame 9. It assumes that the pattern is going to shift a little bit over time, it's going to try adapt its knowledge based on that. So, if the X on this piece of tape is changing perspective, or its motion blur, try to take that into account and continue to track that feature, or that pattern. It's actually a pretty good option to leave as is. There is also Confidence, and what the Confidence means is when the program's confidence drops too low, it does something.

For example, if you set it to Stop Tracking and set to a very high confidence, what that means is it's going to stop tracking if its confidence drops below 100%. And 100% means that it's absolutely sure it knows where the pattern is. So odds are, if I do Stop Tracking at 100%, it's going to stop really quickly. Okay, frame 10, analyze backwards, and it did indeed stop at the next frame. What happened was it was a little unsure of that next frame where the pattern was, it was it's only 98% because it's below 100%, it just stopped.

Now you can have other values too like 50%. If I was to use that, it would probably go much further because it's going to go as long as conference is above 50%. So it goes much further. So you don't have to use these other options, but they're good to know that they're there. Again, the Adapt Feature is quite useful in most cases. I'm going to turn this to 80% also. I think we're good with our defaults here. We'll return to these in later projects, but I just wanted to let you know where these were. So, based on the original settings here, I'm going to click OK, and then re-analyze one more time backwards.

And I'm afraid for this particular project, the first two frames we're going to have to manually adjust. So I'm going to adjust the frame 0 and then go to frame 1 and adjust that. Now we're back to having a pretty good motion path. Now, before I move on, there's one other thing I want to talk about, and that's where the Tracker stores the information. If I go down to shot 1, and expand this dropdown arrow here, you will see there is a Motion Tracker section. You get that as soon as you apply Motion Tracker. If I expand further, you'll see Tracker 1, which we're working on. Even further, you'll see all of the things that are keyframed automatically, includes Feature Center, Confidence, and Attach Point. We talked about Confidence.

Basically After Effects stores the values for each frame. The Feature Center is the center of the feature it's tracking where it is in screen space, and the Attach Point is actually that tiny little x in the center of the Track Point. Now, if you haven't adjusted the motion path manually, the Feature Center and the Attach Point are identical. As soon as you start to move things around though, you can have slightly different values between the too, and that's fine. Now, we're going to return to some of this information later, but this is where the keyframes are actually stored on that layer, and the positions are represented on the screen by these little keyframe boxes.

So, now we have a decent motion path, we can move on and learn ways to apply that motion path to other layers.

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This video is part of

Image for Maya Rendering for After Effects Composites
Maya Rendering for After Effects Composites

34 video lessons · 5227 viewers

Lee Lanier
Author

 
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  1. 2m 0s
    1. Welcome
      47s
    2. Using the exercise files
      1m 13s
  2. 29m 49s
    1. Working with image sequences
      7m 24s
    2. Importing reference video as an image plane
      5m 13s
    3. Matching the 3D camera to the video footage
      4m 23s
    4. Lighting the model
      5m 35s
    5. Creating mattes and shadows in preparation for rendering
      7m 14s
  3. 15m 38s
    1. Using the Render Layer Editor
      4m 21s
    2. Splitting a scene into multiple render passes
      6m 6s
    3. Adding flexibility by assigning material and render overrides
      5m 11s
  4. 15m 2s
    1. Creating render passes using mental ray
      3m 50s
    2. Batch rendering render passes: Project one
      5m 24s
    3. Batch rendering render passes: Project two
      5m 48s
  5. 19m 4s
    1. Importing render passes into After Effects
      6m 25s
    2. Recombining render passes in a composition
      6m 31s
    3. Transforming multiple render passes as a single unit
      6m 8s
  6. 48m 7s
    1. Setting up a motion tracker
      5m 17s
    2. Using a tracker to analyze motion in footage
      3m 56s
    3. Adjusting tracker options for better results
      7m 2s
    4. Matching layer motion by applying tracker data
      6m 26s
    5. Refining a layer's transparency with rotoscoping
      6m 45s
    6. Improving layer movement with the Smoother tool
      5m 7s
    7. Improving the CG by adding blur and effects
      8m 7s
    8. Adding shadow to make the composite believable
      5m 27s
  7. 32m 36s
    1. Recombining render passes for project two
      5m 17s
    2. Removing unwanted elements with a garbage mask
      4m 57s
    3. Applying motion tracking data to a null layer
      6m 38s
    4. Adjusting shadows and matte edges
      8m 12s
    5. Using color correction to improve layer integration
      7m 32s
  8. 25m 46s
    1. Stabilizing shaky video with the Tracker
      8m 2s
    2. Tracking rectangular elements with the Perspective corner pin option
      5m 31s
    3. Adjusting corner pin points and paths
      6m 56s
    4. Applying corner pin data to multiple layers
      5m 17s
  9. 1m 16s
    1. Next steps
      1m 16s

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