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mocha has always been very popular as a tracking tool, but with the rising interest in stereo 3D conversion, its rotoscoping capabilities have become a favorite player in that pipeline and sales have soared. In this course, Steve Wright covers the basics of operating mocha, as well as advanced tracking and rotoscoping techniques. The course also covers the mocha/Nuke stereo 3D production pipeline in detail.
I've mentioned a few times how the planar tracker can introduce a bit of a drift over the length of a track. The Adjust Track feature is designed to compensate for that drift. First, let me do a watch-only demo to give you the big picture before we do it together and I am reusing the building tiltup clip. So I am going to draw a tracker right here, tracking spline and before I started tracking I am going to set the track Motion to Translate only and then I will start the tracker.
By restricting the Motion to Translate only the tracker will have more drift. This will allow me to give you a better demo. The drift comes into the fact that it's comparing adjacent frames and frame after frame after frame are small error slowly builds up and we get our drift. Okay, the tracking is done. We will jump back to frame 1 and I am going to rename my spline tracker. I am also going to turn off the tracking cog so we don't accidentally retrack this later.
Selecting my tracking spline I am going to turn on the Stabilize feature. The View or Stabilize feature will hold whatever spline you have got track steady in the frame. It will compensate for translation and scale but not for rotate or perspective. This makes it much easier to see when we are to locked on. I will stop this. I want to get in a little closer so we can see it better. So I want to move in here. Now I am going to turn on the planar surface. First, I will jump to frame 1, turn on the planar surface and I am going to carefully line it up.
So, each one of these corners is on a pretty visible spot that makes it real easy to see if we have drifted. Okay, you are the watching that the zoom window is over here. Okay, there we go. All right! Now I am going to play this and we can see that the planar surface is drifting off the target. You have quite a bit of drift down here. That corner is really bad, this is a little bit. This corner is not so bad, but we have lots of tracking drift. So let's fix it with the Adjust Track.
Stop that and jump to frame 1. Now I went to frame 1 because that was the frame that I used to line up the planar surface. So at this point the planar surface is at its perfect position. We then select the Adjust Track tab and we are now on a master frame. This is sort of like a keyframe. The difference is as you can see I get these little red Xs and if I move one frame off they go away. So the mater frame is the reference by which all the tracking drift will be calculated relative to.
You will notice as I select each of the reference points. they're still exactly on target. However, if I scrub to the end of the timeline, you can see it drifted rather badly off. Watch the current frame here compared to the master frame there. So that's my reference. This is where I am right now. So I am going to grab this point and readjust it to get it right back adjust it to give it right back exactly like the master frame.
This point now has drift compensated over the length of the shot. I will do the same thing for this point here. look how far this one is off. Okay, so I am going to reposition that one, come down here, reposition this one and this guy, it's gone out just a little bit. Fine! Okay. So we went to the last frame where the drift was the worst and adjusted the reference points to compensate for it. All right! We will go back to our Track tab and now when we play the clip we can see that the planar surface stays locked onto the target very nicely.
We will stop this and jump to frame 1. Now, let's see what happens when we attach our roto spline to this tracker. I will turn off the planar surface. I am going to draw a new spline here. This would be my roto. And again I am choosing real sharp corners to make it real easy to see the tiniest amount of drift. Get these points speeded up here watching the zoom view.
Make sure I get them right in there. And I am going to name this my roto and of course the roto has no tracking data. So now I am going to link the roto to the tracker. Again, roto is selected here, Link to Track and I will select the tracker spline. Now watch what happens when we play the clip. My roto spline is drifting off exactly like the planar tracker did before I did the Adjust Track.
The reason is I have not told it to use the adjusted track data. By default, it uses the original track data just. Just to show you a clear case, I am going to slide the playhead all the way down to the end. Now, watch what happens when I tell it to use the adjusted track from the tracker. Watch the spline's right side. See, that's the correction that it got from the Adjust Track. And now when I play the clip my roto spline stays locked on to the target. We will stop that.
In this example, we used Adjust Track to remove the drift from the tacking spline. You will see surely that we can also use it to remove any drift in the roto splines that are linked to it.
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