OPERATION
Options Window
350-9047 v3.0.1 DGy Model 201x User’s Guide 47
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•Threshold - When edge differences between blocks in
successive frames exceeds the threshold value, a change is
registered. The threshold value may be set to a number
between 0 and 255 with a default of 16. A low threshold number
requires small edge differences between blocks to be
considered a change; a high threshold number allows greater
differences before a change is indicated.
SExample: A black foreground airplane against a blue and
white sky can use a high threshold of 240. This threshold
allows the DGy to locate only edges associated with the
airplane while ignoring edges between sky and clouds. The
threshold parameter would have to be lowered, possibly to
50, if edges of a light gray airplane needed to be located
against a medium gray cloud background.
•Interframe Length - The interframe length establishes a
minimum rate for the transmission of a new anchor frame
regardless of the threshold or sensitivity setting. This insures
that even slow, incremental changes are captured. Interframe
length may be set to a value between 0 and 4095 with a default
of 30. Interframe length should be adjusted after threshold and
sensitivity parameters have been set.
To calculate the refresh rate:
Signal frame rate = Refresh rate in Hz
Interframe length
SExample 1: For a frame rate of 15 fps and an interframe length
of 5, the minimum frame update rate would be:
15 =3
Hz or 3 frames per second.
5
SExample 2: For a frame rate of 30 fps and an interframe length
of 59 the minimum update rate would be:
30 = 1 Hz or once every 2 seconds.
60 2
The optimal interframe compression settings for an input depend on the
nature of the image; some experimentation may be required. Set
interframe compression values low for an image with a high degree of
motion; this will keep the motion smooth. Higher settings may be used
for an image with little motion. The higher the interframe length, the
greater the reduction of network bandwidth used.