Quote:
Originally Posted by AgNa
BTW whats a SCHMITT TRIGGER??
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I'll try to explain in a non technical context
Imagine you have a bucket of water (our frame motion difference range) with a single sensor (our treshold) like this:
Code:
| |\ blurring range
| |/
| |<---- Sensor at this point
| |\
| |/ Temporal filter range
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Now we fill it with water (frame motion differences), but it just so happens that the water is barely touching the sensor, and the next frame difference is just barely under the sensor (the water is moving). If this happens on a time lapse (as on your sample), we have one frame difference with one filter(water detected), and the next frame difference with another filter (water not detected)
So you have an oscilation of alternating filters.
The way to fix that, is to add a SCHMITT TRIGGER circuit in software, just like it is designed in digital logic.
So what we do is this: If the water fed (the frame difference) just hit (tripped) over the sensor point, we LOWER the threshold point a tad. For example: If our sensor (treshold) measuring point is 2.0, we drop it (set it) to 1.8 on a "rising" transition of water (frame difference). If the water (frame difference) tripped BELOW 1.8 (lowering difference), we set the treshold back to 2.0.
What does this do
Simple
It avoids oscilations (hysteresis), because once a point is tripped, the water level (our threshold) needs a higher (or lower) level change to switch, and this keeps the filters from switching back and forth (oscilating) on that boundary when that condition is met
I hope this was clear, as I tried to make it as non-technical as possible
If you want a simple technical (digital) explanation, here it is
:
http://www.photonics.com/dictionary/.../QX/lookup.htm
-kwag