Motion Tracking in Adobe After Effects 5.5
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Let’s address each of these in reverse order.
Since a large area of the wide shot is gray, and the label is so small, it might be better to track the footage in reverse. Using the time marker in this window, move to the end of the footage after the zoom has been complete. You should notice how this solves part of our problem. First it is much easier to place the tracking points on the label, and second, we now have some high contrast areas from which to track. If you are doing a project that is similar to this, you should probably put tracking dots (green dots can be purchased from your office supply store). This will save you a lot of headaches, trust me, but there are times when you have no control during the shoot. [an error occurred while processing this directive] Notice the areas where the electrical tape and circuit boards meet. They are strong vertical/horizontal lines with lots of contrast. Move the four tracking boxes to these corner points and resize the Search regions appropriately. Since the footage will be tracked in reverse, the shot will zoom out, so move the Search regions so they are looking ahead to the next frame.
When the tracking boxes are in place, move the tracking points to the corners of the bomb label. These points move in relation to the tracking boxes, so it doesn’t matter if they are right on the corners of the label, just as long as they match the general shape of the label we are covering.
Now let’s deal with the overall contrast and grain issues of the footage.
Clicking on the Options button will open up a new window. After Effects should have already selected the layer immediately above your footage layer to apply the Perspective Corner Pin Effect too.
Make sure the frame rate is correct. Because of the DV compressed video may not contain all of the information we might be able to track in a single frame, turn on Track Fields, this will increase the calculation time, but will produce more accurate and smoother results.
Turn on Track in Reverse since we want to track from the current frame to the beginning of the clip.
For Track Options we should use Luminance. The areas which were selected do not contain much RGB information, but the near black and white regions do have very different Luminance ranges (high contrast).
Because DV artifacts or aliasing can further throw off the tracking data, we can smooth these errors by turning on Process Before Match and turning the Blur amount to 5 pixels. This will only blur the footage for tracking purposes, not the final results.
Change Track Adaptiveness to 50%. This is a pretty good trade off between tracking a particular region compared to the previous frame and tracking a region compared to the entire clip. A higher number is generally good for zooms. A lower number keeps the tracking data fairly loose.
The final item you should change regardless of anything else is Subpixel Matching. Subpixel Matching is how After Effects interpolate and effect to thousandths of a pixel. The smaller the subpixel matching, the more accurate the data. For 99.9% of all tracking and stabilizing projects you will have, you will never, ever use subpixel matching of ½ pixel. Also because of fast processor speeds, you should go take advantage of higher interpolation rates. On my Sony VAIO 800MHz system, I can run this clip at 1/32 subpixel matching fairly quickly. My monster 1.5GHz machine runs those calculations even faster.
Hit Okay, and then Analyze. After Effects will then begin tracking the selected regions in reverse. One of the nice things about tracking and stabilizing in After Effects, is that if any of the tracking boxes start to drift, you can stop the calculations, back the time marker up to the last good piece of data, reposition the tracking boxes and continue the analysis.
If all goes well, click on Apply and the Corner Pinning Effect will be applied to the countdown layer on every single frame.
To add some depth to the clock, add the Bevel Alpha effect to the layer and adjust.
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| Click image to view small QuickTime movie of final composition. |
Hopefully you have learned a little something about tracking data in Adobe After Effects, if you haven’t used this option in a while, perhaps knowing that this feature has undergone some much needed fixes over the last couple of versions may get you to give it another chance.
Stephen Schleicher is the producer for Digital Animators and Digital Webcast. When not running the DMN Central Division, he can be found in front of his computer shouting, "Render faster!" You can contact him at stephens@digitalmedianet.com.
Source: Digital Media Online, Inc.
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