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Thread: After effects motion tracking question

  1. Default After effects motion tracking question

    I want to motion track something onto a box i'm holding in my hand, but my hand is covering parts of it. I understand that i should mask out my hand, track the mask, track it on, and copy the mask onto another layer on top right? How do I mask out my hand if it moves (changes shape when i let go, fingers, etc)? Do i have to do this frame by frame?
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  2. #2


    Your talking rotoscoping here. You don't need to do it frame by frame, but don't try to do the full hand at once. First of all it is good practice to create your masks on a new solid layer, then use that as a track matte. It can be very usefull when compositing and becomes very usefull later for more advanced techiques and is a good habit to get into.

    Work with masks with small numbers of points, a tweaked circle/oval is a good place to start. Mask off a phalanx of a finger, set a key frame, go to the end of the timeline, realign the mask and set a new key frame.

    Now scroll through the timeline looking for the point where the finger and the mask go furthest out of alignment, reposition your mask and set a new key frame.

    You'll notice that with just these three key frames your path is starting to take shape. Rotoscoping is largely based on studying the motions, to find the greatest possible ecconomy creating the smoothest possible motion.

    Now do the same thing for the point where the finger and the mask go furthest apart between the first and the middle keyframe, then the last and the (previously) middle. Then continue doing this between each 2 keyframes where necessary untill you have a smooth path.

    Ideally the least amount of keyframes you need the better. And ideally you don't want to be changing the shape of the mask, if you do it can just look very wobbly on playback. That's why you want to build up a number of smaller masks with fewer number of points. There is less need to adjust the shape of each.

    However, you may find that after building your path you do need to tweak the shape of the mask. If so, think carefully about how you can minimise the need for this.

    You really want to learn how to do that way first, but you can track the object you want to rotoscope, mask it (creating a matte on a new layer) then aplly the track data to the matte. I.e. the matte follows the track. Only for the simplest motions will it be that straight forward, a mixture of these 2 techniques is way more likely.

    Last edited by david walsh; 02-04-2011 at 09:04 AM.

  3. #3


    David's given you a lot of good tips here. There is more information about rotoscoping in After Effects here.
    Todd Kopriva, Adobe Systems Incorporated
    After Effects Help and Support
    Premiere Pro Help and Support

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