Latest post Thu, May 31 2018 1:41 PM by Bruno M. 1 replies.
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  • Mon, May 28 2018 10:54 AM

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    Beyond basic tracking.

    Having recently had month to mess around with the Mocha Pro plug-in for MC,  I began to wonder how much could be achieved with the native trackers in MC. While Mocha is fantastic, both to work with and in what it can do, it made me realise how little I know about the MC trackers.

    I know the basics of copying the tracking data from one effect to another. I know I need two trackers for zoom/depth of field tracking. I know I need 4 trackers for corner pinning but there are some things I am curious about.

    Is there any benefit in using two or more trackers in tracking one object?

    If I track two or more objects in the one scene, how do the two trackers interact with each other, if at all. In other words, are the two trackers used to track a zoom movement, a specific pair or would two independently tracked objects, moving away from each other in the X axis, fool MC into thinking a zoom in in Z was happening?

    Can rotation in the Z axis be tracked by using more than one tracker?

    Is there any benefit to be gained from increasing the area being tracked to cover a large flat surface, as opposed to the small standard tracking box?

    Mainly I’m curious of any benefits of using more than one tracker and whether they would cancel each other out, average out or corrupt the overall data.

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  • Thu, May 31 2018 1:41 PM In reply to

    • Bruno M
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    Re: Beyond basic tracking.

    I'm not sure from your question whether you're referrring to MC's point trackers or the Mocha planar tracker.

    As the name suggests, point trackers are using a pixel pattern (as defined by the inner box) that needs to be searched for in successive frames. The search area is defined by the outer box, so the larger the search area, the longer your track will generally take. You can increase the size of the inner box to include more pixels, but I haven't found this tends to improve the track accuracy. All the point trackers I've seen tend to assign the number of tracking points based on the type of track required, as you rightly pointed out in your post. If you have two tracks moving away from each other, I don't think the software assumes anything about moving through Z space, it simply applies this same movement away from each other to whichever shot you've designated as being altered by the tracking data.

    Mocha is a planar tracker, so you're not defining points but an area to be tracked. Mocha tracks the pixels within this area and can 'sense' if there's simple X-Y movement, or something more complex than includes rotation, size, shear and perspective. This makes it a much better tracker for complex moves, as well as making it reasonably immune from focus problems and smaller objects obscuring the track - things that would generally defeat point trackers. It can only do this if enough of the basic area to be tracked is still able to be recognised, so the larger area you can assign to the plane the better the track.  Therefore it's a perfectly acceptable practice to draw two or more areas to a plane to improve the accuracy of the tracker. The beauty of Mocha is that you can stop the tracking operation at any point and re-define the tracking area (to remove areas that might be causing problems) and then resuming the track. With Mocha you can also draw a further area on a track above, and this will instruct Mocha to EXCLUDE this area from the tracking area. This is particularly useful where you have reflections on an object, as these would normally not be on the same plane as the object and could throw the track off. An example of this would be tracking a mobile phone. You can draw an area around the whole phone, but the reflections off the black screen would likely produce a poor track. by drawing an area around the screen reflections, Mocha will ignore all data in this area and give you an accurate track.

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