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Working with AGC and Open Shutter Settings
The SpeedDome Ultra VII Day/Night dome provides settings for compensating for low-light scenes
in color: Automatic Gain Control and Open Shutter. Automatic Gain Control (AGC) amplifies the
video signal in scenes with minimal light. Many low-light scenes result in picture noise. As gain is
increased, the picture noise is also amplified.
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. For more information, continue with Understanding How
Advanced Shutter Settings Improve Low-Light Performance.
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 3–5 illustrates a Shutter Limit of 1/4.
Figure 3–5: Graphical view of Shutter Limit settings
Red Light Red Light Red Light Green Light
180
msec
250
msec
250
msec
Configuring Camera Features 3–7