Software User’s Manual Ver.A1D-502-V8.03.30-NB
54
Trigger threshold
Look at the moving object entering the area of motion detection: although moving
quite slowly, it caused motion activity
–
several pixel regions reported a motion that
was faster than allowed
“
speed limit
”
of sensitivity (70).
A 10% trigger threshold means, 10% of this motion detection area were filled with
moving pixels at that moment. By visual observation you can also see that the object
standing inside the motion detection region indeed covers about 10% of its size.
What if the object is really small but moves rather fast (gets triggered by the current
sensitivity level)? For example, we want to detect people but not the cat walking in
the room. Although both people and cat may move with the speed that will trigger
motion, they have different size of triggered pixels. For example, a human passing
by the motion detection region will trigger 25% of pixels in that region while the cat
would trigger only 2%. Since we want to have a real alarm in case of human or
vehicle passing by while ignoring birds, cats, butterflies, mice, etc, we need a filter
that can define how many percent of triggered pixels will be considered as a real
alarm. This parameter is called trigger threshold. The default value of trigger
threshold is 10%. It means, only the objects that are bigger than 10% of the motion
detection region size and move faster than allowed by sensitivity level (70) will
produce actual alarm.
How to choose the most optimal trigger threshold level? The rule of thumb, keep
the trigger threshold as small as possible while not causing false alarms by
the moving objects that are not humans or vehicles.
You can have different sensitivity level and trigger threshold level for each motion
detection region.
In order to understand all of the above even better, please refer to the table below
containing four possible combinations of settings using sensitivity level and trigger
threshold percentage.