American Dynamics SpeedDome Ultra 8 Operator's Manual page 36

When AGC is enabled, the camera automatically adjusts the gain setting value. When AGC is
disabled, no gain is applied to the video signal. This may make the video appear darker on the
monitor.
The gain setting for the camera differs from the maximum gain (Max Gain) setting available
on the Camera Functions menu. The Max Gain setting is an upper limit for how much gain
can be increased when AGC is enabled. The trade-off between picture level (brightness) and
noise may be adjusted by setting the Max Gain value. Lower values for Max Gain setting
may result in a darker picture with less noise. Higher values for Max Gain setting may result
in a brighter picture with more noise.
In addition to the AGC settings, you may also adjust the Open Shutter settings to improve
dome performance in low light situations.
Understanding How Advanced Shutter Settings Improve Low-Light Performance
The camera dome supports the ability to view color images from extremely low-light
situations. This feature is called Open Shutter and is only in effect during low-light situations
where an image would not be obtainable otherwise. It does not affect the camera performance
in normal or bright light situations.
When the Open Shutter is enabled and the scene illumination is too low to obtain a clear image
at the normal video rate, the camera collects luminance information from multiple fields. As it
does so, the current video information is retransmitted until new information is available from
the camera. Under these conditions, moving objects will appear blurred, and still images may
appear blurred, choppy, and with more static than video obtained under normal lighting
conditions.
The Shutter Limit value sets the video update time in fractions of a second. Depending on the
lighting conditions, the video information may be updated more frequently, but no slower than
the limit set.
Figure 24 illustrates a Shutter Limit of 1/4.
In this example, the dome receives information about the color of the traffic light. While the
light is red, the image is relatively static. With the shutter limit set to 1/4 second (250
milliseconds), updated red light information is transmitted at 1/4-second intervals. When the
light changes from red to green, updated light color information becomes available. The dome
must now transmit information about the green light. This update occurs as soon as the green
light information is available. This may occur before the 1/4-second interval elapses. In this
example, the light changed to green after 180-milliseconds. Thereafter the green light
information is transmitted at 1/4-second intervals until new light color information becomes
available.
If the light were to change from red to green halfway through the field integration interval (125
milliseconds), it may appear that both the red and green lights are on simultaneously. This
situation is illustrated in Figure 25.
SPEEDDOME ULTRA 8 CONFIGURATION UTILITY
OPERATOR'S GUIDE
Figure 24. Graphical view of Shutter Limit settings
250
msec
34 of 140
250
msec
180
msec
8200-0600-01, REV. B