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Strobelight77
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Motion Tracker losing track

Feb 24, 2012 1:16 PM

Tags: #after #effects #track #motion #tracker #losing

Hi,

 

I'm new to AE and just running some simple tests with the motion tracker.  I'm running into all kinds of trouble on something I think shouldn't be that big of a deal.

 

Here is an example - I've tried single and multiple black dots on a well-lit hand.  Regarless of tracker settings, number of tracking points, or size of the tracker it ALWAYS loses the track quite significantly (see image below).

tracker test.jpg

What am I doing wrong?

 

Much appreciated!

1046 Views   8 Replies   Latest reply: Strobelight77, Feb 26, 2012 8:59 PM
 
Replies
  • Dave LaRonde
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    1. Dave LaRonde,
    Feb 24, 2012 1:55 PM   in reply to Strobelight77
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    AE's Online Help has good instructions and good advice to follow when motion tracking.  Since you're new, it wouldn't help much to write this stuff out in AE Lexicon, because you wouldn't understand it!  There's a lot to the process, so you might as well have pictures to go along with words.

    Here's an overview of the process.

    Here's the workflow to follow.

    Here's how to correct a motion track. Problems like yours above happen all the time.

     

    The overview especially has some very helpful links.  And take the time to read this stuff carefully, okay?  It's easy to get lost when you're new. Read them in the order they appear.

     

    And since you're new, this is also extremely helpful:

    http://blogs.adobe.com/toddkopriva/2010/01/getting-started-with-after- eff.html

    
     
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  • Strobelight77
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    2. Strobelight77,
    Feb 24, 2012 2:13 PM   in reply to Dave LaRonde
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    Hi Dave,

     

    Thanks, but I've been through that information.  Perhaps I'm simply expecting too much of AE.  While I'm relatively new to AE I've used a wide range of software packages for quite some time on a variety of platforms.  Boujou can whip this off without any problem for example.  I would have thought that a black dot (or several) on skintone would not be a problem for AE, so this drift (more like massive jump) is surprising.  I guess I'll have to adjust my expectations.

     

    Thanks

    Steve

     
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  • Rick Gerard
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    3. Rick Gerard,
    Feb 25, 2012 5:05 AM   in reply to Strobelight77
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    Your tracking areas are most likely way too small. This looks like standard def video and it looks quite compressed. All of that noise, the compression artifacts, and the tiny tracking areas confuse the tracker because it's averaging the pixel information in the track area, not looking at a single point.

     

    I'd try tracking the hand in Mocha. I'd also probably try tracking some different areas of the hand like the crevices near the thumb, the spaces between the fingers.

     
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  • Mylenium
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    4. Mylenium,
    Feb 25, 2012 7:50 AM   in reply to Strobelight77
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    AE's tracker is built around a simple thresholding and pattern detection algorithm, which by today's standards is not up to snuff. As Rick suggested, try mocha. If you realyl want to stick with AE, try crosses instead of just dots...

     

    Mylenium

     
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  • Strobelight77
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    5. Strobelight77,
    Feb 25, 2012 11:44 AM   in reply to Strobelight77
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    Thanks Rick and Mylenium,

     

    Actually the footage is HD - I just cropped and down-sized it.  In any case, it sounds like AE isn't the way to go for tracking which is too bad as it requires adding another step.

     

    I'll give Mocha a try.

     

    Thanks again,

    S

     
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  • Dave LaRonde
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    6. Dave LaRonde,
    Feb 25, 2012 7:27 PM   in reply to Strobelight77
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    With a simple track like you posted, there is no reason why AE would not have been able to do it.  Perhaps there is something about this particular piece of video that makes it difficult.

     
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  • Rick Gerard
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    7. Rick Gerard,
    Feb 25, 2012 10:01 PM   in reply to Strobelight77
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    I'm sure it's your tracking dots. I've tracked hands before and it takes about a quarter of an inch in a dot or a triangle to get a track. There's just not enough contrast on the shot for AE to find anything to track. Here's what I'd track using position, rotation, scale. It should work as long as the fingers stay open. Notice the size of the tracked area and the details in the shot.

     

    Screen Shot 2012-02-25 at 9.48.46 PM.png

     

    Those tiny black dots are just way too small. You need about 200 to 400 pixels of detail to get a good track. Your dots are only about 12 pixels. That's too small of a sample to get an average. Here's the dot viewed at the pixel level.

     

    Screen Shot 2012-02-25 at 9.55.13 PM.png

     

    Imagine how that single dark pixel in the middle of the shot is going to dance around when the hand moves. Here's the same shot moved only 1/2 pixel.

     

    Screen Shot 2012-02-25 at 9.59.04 PM.png

     

    You can see how different the data is. There's just no way that a tracker, any tracker, could hold an accurate sample on such a changing target.

     
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  • Strobelight77
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    8. Strobelight77,
    Feb 26, 2012 8:59 PM   in reply to Strobelight77
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    Thanks, Rick.

     

    It was the size of the dots.  The points you suggested aren't practical because the fingers are in motion so those points aren't consistent.  However, I worked out a larger tracking target and the track held at a much more respectable rate.  Still needed some tweaking, but it's much better than it was.

     

    Thanks to everyone for the input and suggestions.

     

    Steve

     
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