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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.
The Track tab over here has several seeing that you can refine to improve your tracking results. I'm using the whip pan movie from the Lesson_04_Media file. Let's start by taking a look at the Preprocessing section here. In order to get the options lit up, I'm going to have to first draw a spline, so we'll just draw a little something here, and now all the settings light up. The Input Channel selection here determines what the Tracker is going to use to track on the image. The default is Luminance which means that the Tracker is going to make a black-and-white or a luminance version of the image and then track on that.
However, there are some situations where you don't get good results with that and that's mainly when you have an image that is very strongly dominant in one solid color, like a very blue picture. In that case, select Auto Channel and mocha will look at all three channels and pick the one that has the best contrast, easiest to lock onto. Next, over here the Minimum % Pixels Used. When I drew this shape, it came up with a number of 90%. What that means is mocha is going to use a 90% sampling of the pixels inside my shape to do the tracking calculations.
However, if you draw a large shape like this, mocha chooses a smaller percentage, 30%. The reason is to save processing time. Usually, this is a wise strategy. But if you have trouble locking onto the target, you can try increasing this percentage. It'll slow down the tracking time but you'll get better tracking results. To look at Smoothing, I'll need to draw a new shape, so I'm going to turn these off.
Let's take a look over here. Okay, let's say we need to track on this wall back here. I'm going to set an In point here and move the playhead a little bit and set an Out point there. Okay, so I'll track on that wall in this little section right here and see what happens. I'll draw my tracking shape. By default, the Smoothing Level is set to 0. The Smoothing Level is how much of a blur mocha will apply to the tracking image before doing the tracking.
So a Smoothing Level of 0, no blur, so let's track it to see what we get. Okay, we got a nice track. No problem. Now I'll go back to the beginning of that section and I'm going to set the Smoothing Level upto 10. Now that's going to blur so much of the detail out of this picture, the Tracker won't be able to lock on. Let's see what happens. Ooh and there we go. Tracking terminated prematurely. All right! So there you go.
The reason you might want to do this is if you were trying to track some particularly noisy footage, you can try raising the Smoothing Level a little bit, hoping that you knock out the noise with a grain before you knock out the critical detail of that the Tracker needs to track on the image. Next, let's take a look at Motion, specifically over here the Large Motion and the Small Motion. We've already looked at the Tracking motions over here in a previous video as well as already looked at Manual Track. So we'll just concentrate right now on Large Motion and Small Motion.
Large Motion means the Tracker is expecting large motion in the clip, so it's going to search a wider area looking for a fit. Small Motion is for the scenario where there's very slow movement in the plate, so the Tracker only has to look a short distance. This will speed up or optimize the tracking. It won't get you better tracking results. But we can illustrate this with an example. I'm going to turn off Layer 3, here are my In and Out points, and move down here to look for this target here, pan down a little bit, and I'm going to draw a little tracking shape around the target.
And again, the Planar Tracker doesn't care if the shape was out of frame. I'll set my In point here, track forward for a little bit, and sure enough, the Tracker has no problem at all locking on. All right! So let's try that again. We'll bring the playhead back to the beginning of my section. I'll set it for Small Motion and now the Tracker will only be looking for very small movements and it could get lost. There we go! We'll stop that.
So the Tracker immediately got lost because the motion in the plate was big and it was looking for small motion. So I'll put that back to the default, Large Motion. Next, let's take a look at the Search Area features. The Horizontal and Vertical values here determine how many pixels on either side of the spline that the Tracker is going to be searching. With the Search Area set for Auto, the Tracker determines how big the Search area will be based on the size of the image.
But you can change that. I'm going to use the same shape I drew up here, I'm going to clear all the tracking data, put it back to Large Motion, and I'm going to set this Horizontal to a small value like 2. Now the Tracker is only going to look 2 pixels every frame and it will not be able to lock onto the target. And there we go. it got lost immediately. Okay, so we'll leave that on Auto. Of course, the same applies for Vertical, if you had a very fast tilt-up, you might want to adjust the values here. The Angle: if you are tracking a rotating object, the Tracker has a certain default number of degrees of searching on a frame by frame basis.
If you find that it's not locking on, you can increase the Angle and it will stay locked onto a rotating target. If the target was rotating let's say 180 ? in 10 frames, then that's going to be about 18? per frame. And the default is a much smaller number, maybe 2? or 3?. So you would look at the Rotation, count how many frames, do a little math to come up with a larger angle that the Tracker should be looking for, frame to frame. Again that's just a search angle. Same thing for zoom, the Tracker does look for zooms, but if the zoom is very fast or very rapid, then the default zoom it's looking for might be exceeded.
So you might have to dial up that zoom number. And the last is the Export Data. We'll be looking very closely at how to export data in an upcoming video.
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