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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 3–6.
Figure 3–6: Mixed field integration
Red Light Red Light Red/Green Light Green Light
125
msec
250
msec
125
msec
Adjusting the Shutter Limit sets the update time used to maintain the image quality. If you want to
videotape an incident in low-light conditions, you may find that tape quality is not acceptable. To
ensure that the videotape quality is acceptable for possible prosecution purposes, you may want to test
the Shutter Limit settings under the expected lighting conditions.
The Relationship between IR Mode and AGC and Open Shutter Settings
The current IR Mode setting affects which AGC and Open Shutter settings are available. The
following table lists which AGC/Shutter modes are available based upon the IR Mode setting:
IR Mode Setting
AGC Off
AGC On
Open Shutter
Off
Yes Yes Yes
On
Yes Yes Yes
Auto High
Yes Yes
No
Auto Mid
No No
Yes
Auto Low
No No
Yes
In addition:
• When AGC Off is the current setting, the Max Gain and Limit fields are not displayed.
• When AGC On is the current setting, the Max Gain field is displayed and may be modified. The
Limit field is not displayed.
• When Open Shutter is the current setting, both the Max Gain and Limit fields are displayed
and may be modified.
3–8 SpeedDome Ultra VII Day/Night Operator's Manual