Motion Stabilization
When I teach I often have to remind my students that shooting on a tripod is the best way to make sure the shot is going to be stable. Do students ever listen? Did you ever listen to your instructors? Most of the time yes, but occasionally they get too excited about a shoot and forget everything they have been taught.
In those instances where you have a shot where the videographer (or even cinematographer) has forgotten to use a tripod (or couldn’t) and the camera shake is very noticeable, you can use After Effects from Adobe to correct the problem. [an error occurred while processing this directive]
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| Click image to view raw footage. |
After importing the footage into After Effects, place it in the Timeline and right click the newly created layer. Select the Motion Tracker/Stabilizer from the pop up menu. This will open the Layer Window with Stabilizer controls already available.
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| One way to access the Motion Tracker/Stabilizer function in After Effects. |
The footage in this exercise not only moves up and down and back and forth, it also wobbles slightly from side to side. If positional movement were all we were concerned about, we could leave just that option selected. But because of the slight rotation we’ll have to select both position and rotation tracking.
When rotation tracking is turned on, two motion tracking boxes appear in the Layer window. Each of these represent the tracking regions After Effects will use to stabilize the footage. The inner box is the Feature Region, and represents that element in the image you are tracking. The outer box is the Search Region, and represents the area of the image After Effects will be looking for the tracked element to move to.
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| The inner box represents the Feature Region, while the outer box represents the Search Region. |
The Feature Region and Search Region boxes can be resized to accommodate movement and tracking, but don't make them too large, as it will take longer to calculate. The left-most tracking box represents the position data, while the box on the right (by default) and the line between it and the first box will calculate rotation.
Position the tracking boxes anywhere in the image, but make sure the Feature Region boxes have something to track. Areas of strong contrast are best.
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| Areas of strong contrast work best when placing the tracking boxes. |
Once positioned, open the Options panel and make adjustments according to your needs. In the case of the wall, the default settings are pretty good, except for the way After Effects is interpreting the tracked points. In this instance, tracking based on luminance will work best because of the contrasts between the dark and light portions of the stone. The only other setting that needs to be changed is Subpixel Matching. This determines how closely After Effects will interpret the Feature Region, and how accurate the tracking results will be. The smaller the Subpixel Matching, the greater the tracking, but at the expense of processor time. You will have to see what your system can handle, but you should always try for a value of at least 1/16, with 1/32 being the preferred. For more information on the options in the Motion Tracker/Stabilizer, check out Tracking a Countdown, which discusses using the Tracking options in After Effects.
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| Try to set Subpixel Matching to at least 1/16. If you have a fast system, use 1/32. |
When the settings have been adjusted to your liking, run the analysis on the layer. If all goes well, then you simply need to apply the data to the layer in the Timeline.
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| Click image to view stable footage. |
It does take some time to calculate, it can be frustrating based on the quality of the footage you have been given, and it will take some time to get used to, but the results of using the Motion Tracker/Stabilizer in After Effects can be well worth the effort.
When not working deep in the labs of the DMN Central Division testing the latest and greatest software/hardware products Stephen Schleicher can be found at the local university teaching a few courses on video and web production. He can be reached at schleicher@mindspring.com. You can also visit him on the web at www.mindspring.com/~schleicher.
Source: Digital Media Online, Inc.
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