ACTi V11 User Manual
Page 50
Encoder Firmware User
’s Manual H1.02.30
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).
The blue graph on the right side of the
image shows how many percent of
pixels within the motion detection
region were considered as
“currently in motion”. The activity panel itself is a timeline – for each
moment of time you can see the height of the blue bars. You may notice that at certain moment
the tallest bars in the activity graph reached about 25% (a quarter of the total height in activity
panel)
– it means, 25% 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 25% 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.