Performing a track
Video: Performing a trackNow that I set up a good Track Point, next I can actually perform the track, but before you tell After Effects to go track this shot, it is essential that you open up the Options dialog in the Tracker panel. This contains an important set of parameters that After Effects will use while performing the analysis and track. You can rename it if you want such as first attempt - cloud. Adobe has left a provision for third- party Tracker plug-ins, but as of the time I have recorded this, none exist. Most important is this Channel dialog.
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Explore how to use the motion tracker and stabilizer built into After Effects and shows how to handle a variety of shots. Author Chris Meyer leads a quick tour of the third-party software mocha and demonstrates the workflow for The Foundry's KEYLIGHT, both bundled with After Effects. The course also covers tracking a greenscreen shot with a handheld camera and replacing its background.
The After Effects Apprentice videos on lynda.com were created by Trish and Chris Meyer and are designed to be used on their own and as a companion to their book After Effects Apprentice. We are honored to host these tutorials in the lynda.com Online Training Library®.
- Understanding motion stabilization and keying
- Performing a track
- Applying tracking to effects
- Keying with KEYLIGHT
- Replacing images
- Improving the composite
- Garbage masking
- Dealing with interlaced footage
Performing a track
Now that I set up a good Track Point, next I can actually perform the track, but before you tell After Effects to go track this shot, it is essential that you open up the Options dialog in the Tracker panel. This contains an important set of parameters that After Effects will use while performing the analysis and track. You can rename it if you want such as first attempt - cloud. Adobe has left a provision for third- party Tracker plug-ins, but as of the time I have recorded this, none exist. Most important is this Channel dialog.
What is the contrast inside the feature region that you're tracking? Is it a difference in Luminance? Well, in this case, we'll have a bright speck of cloud against a dark background; Luminance is indeed what I want to track. There will be other occasions where you'll have a bigger contrast in color. So make sure you set up channel according to what feature you're tracking. Process before match comes in handy if you have got particularly noisy or blurry footage. If the footage has a lot of film or video noise in it, you might want to pre-blur it, so After Effects does not accidentally track those grains of noise.
On the other hand, if your shot is particularly soft or out of focus, you might want After Effects to enhance or sharpen this shot to give it more contrast actually track. Most shots, you don't need this and I will leave it off. If your clip is interlaced, in other words, there are separate fields on each frame of the shots and there is movement between those fields, you want to enable Track Fields to pick up that inter-frame movement. You always want Subpixel Positioning to be turned on, leave that on.
Adapt Feature On Every Frame only comes up if you have a lot of change in the shot. For example, if you are zooming in or zooming out, if the object that you are tracking is moving further away or coming closer to you, there's basically changing perspective or changing size, then you want to adapt the feature on every frame. Again, there will be minor changes in the shot, I'll leave it off. Finally, you can give After Effects a hint of what to do if it loses confidence that it has indeed found your feature region in the next frame.
This pop-up contains several choices. Continue Tracking basically says it's not going to get any better than this; keep going. Stop Tracking says oh, if there's a problem because you've lost the track, let me know. Extrapolate Motion is useful if something obscures your feature that you want to track, in other words, if someone walks in front of your particular feature and we will use that later in this lesson. And finally, there is Adapt Feature. Basically it says don't change what you are looking for from frame-to-frame, unless it changes so much from where you started that you have less than 80% confidence.
Then on that one frame, readapt to what you have found and continue using that shape from this point forward. Again, this shot has very little motion in it, but this isn't a bad for setting to try on a lot of your tracks. And by the way, if you have troubles with the track, all is not necessarily lost. You can undo, come back and try different Tracker Options to see if you get better results. I will click OK and now that I have done that, I can go ahead and analyze my clip. If I chose to start on the last frame of that clip, I will go ahead and analyze backward.
If I want to just move a frame at a time to make sure After Effects is finding its way, I will go one frame at a time; these two buttons. Well, in this case, since I have started in the very first frame of the clip and I want to do the entire clip, I want to go ahead and analyze forward. I will click on this button and watch After Effects do its thing. And since I have already cached this clip into memory because I previewed it, it actually went by pretty fast. A lot of the time involved in motion tracking is just in reading the file off the drive, and this is the reason why you want to have your assets on a fast drive, or go ahead and perform RAM previews to load your clips into RAM.
Okay, After Effects finished already and I can start to see a little hint here of the path it followed while stabilizing this clip. At this stage is just tracking a feature. We haven't stabilized yet. As I go ahead and drag the time indicator through which shows how After Effects is adapting to that feature from frame to frame. Now if I wanted to, I could go ahead and zoom in and see that path in much greater detail. Now I can see the After Effects is actually moving by fractions of pixels to track motion in the shot. I will zoom back out press the spacebar and reset of my shot.
It's a good idea at this point to save. This track information is saved as keyframes in the timeline. If I press the U, you will see all my keyframes down there. This is how After Effects saves track information with your project. So after I perform and analyze, I will save our project at this point to make sure I have indeed saved all these keyframes that After Effects has calculated for me.
Find answers to the most frequently asked questions about After Effects Apprentice 12: Tracking and Keying .
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- Q: This course was updated on 12/12/2012. What changed?
- A: We added new chapters on the Warp Stabilizer and the exciting new 3D Camera Tracker, and new movies on the Tracker panel, converting to ray-traced 3D, and rolling shutter repair, all new features introduced in After Effects CS6. In addition, there are new sets of exercise files designed for After Effects CS5.5 and After Effects CS6 and a companion movie that shows our premium subscribers how to use the exercise files.
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