Expert: Andre Hickman - 3/24/2007

Question
Hello,
I have river clips which were shot on the boat, so a little of it shake. I try to use "tracker control" in After Effect Pro but I'm sure about "feature region ; search region and attach point". Please tell me how do they work ?
Thank you so much.
Have nice weekend !

Answer
I am assuming that you are using a tracking control in the MOTION STABLIZER.  I'm not going to give you a technical explaination, but rather a pictorial one, that hopefully will help you understand.  

Say for instance, you have footage of a persons face, and you want to track the pupil of their eye, because you want it to glow red.  They have distincte blue eyes.  You would want to focus on the area around the eye, everything else in the picture doesn't matter.  That would be where you create your feature region to encompass..the area the covers the eye, eyelids, etc.  

Now you know that what you are searching for is a small black area that is surrounded by blue (blue eyes) so your search area is going to be contained in the feature region, and you'd cover the blue iris of the eye and the pupil.  This minimizes the area that the computer has to search, and gives it something to focus on.  

The attach point is placed exactly where you want "attach an effect or track.  

You want to start your tracking in a good segment of video where your subject or Feature region is pronounced, and in full view.  If it ever goes out of view, then the computer can't find the pattern of colors that it is looking for...For instance, if the person blinks, now you lose the black area surrounded by blue.  The tracker loses what it is tracking.  

For your shake problems you want to find some feature in the footage that is distinct enough to follow, that stays in view during the time of shaking that you are trying to correct, and start there.

I hope this somewhat simple explanation of the technology helps you understand it better.  If you have any more questions, feel free to ask.

Cheers,
Andre'