Feature Extractor Intro

I’m currently busy working on a feature extractor for my final year project. I’m doing an outdoor surveillance system with shape classification. Currently I’m using a sigma delta background estimation algorithm (removes areas of constant motion from being picked up) to create a background and variance frame and then using those two frames and a difference frame (current frame – background frame), i get a resultant motion frame, the upper right frame in the below image.

Feature Extractor - Background

What i need to do at this stage is “simply” extract the resultant silhouette, convert it into a numeric format: i intend on doing this by finding the centroid of the silhouette and get the lengths of a lines from the centroid to the edge in intervals of 2 degrees. Then I’ll take the 180 lengths I have and normalize them to remove any difference in scaling and then run them through a back-propagation neural network (BPN), first to train it and later for the actual classification.

Now the problem is the extraction of the the silhouettes. If i assume only a single object will be present its easy but as you can seen even a single object isn’t guaranteed to be represented by a single silhouette, due to the nature of current gray scale motion detection algorithms you tend to get a lot of breakage in the detected motion. So i have to extract and reconstruct these silhouettes. Sounds simple? Its not…

I’m running short on time and sitting and reading through stacks of journals for ready made algorithms which I’m still going to have to modify isn’t going to help, so with a bit of brain storming with my dad, we came up with a silly, simple solution. Anyone remember the classic computer science problem: traversing a maze? The solution? The right hand method, stick your right hand against the right wall and walk until you reach the end. I’m going to use this method to trace the silhouette outlines and then do a horizontal and vertical comparison on the separate silhouette outlines and then try a uninformed reconstruction. This is all just an idea right now and i’m not even sure if it will work and if it does whether it will be good enough to use in the final project.

I should actually get back to working on it. Hopefully by the end of the weekend, I’ll have more details and source code of my results. The worst part is that I’m not sure i have the processor time available for this technique, the current motion detection is expensive enough as it is. On my home X2 5400, it takes around 60-70% on the one core.


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