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Understanding
This
ight situations where an image would
al or bright light
nder
tions, moving objects will appear blurred, and still images may appear blurred, choppy,
: Graphical view of Shutter Limit settings
How Advanced Shutter Settings Improve Low-Light Performance
The camera dome supports the ability to view color images from extremely low-light situations.
feature is called Open Shutter and is only in effect during low-l
not be obtainable otherwise. It does not affect the camera performance in norm
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. U
these condi
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 3–1 illustrates a Shutter Limit of 1/4.
Figure 3–1
180
msec
50
msec
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
r
s
msec
250 2
the green light. This update occurs as soon as the green light information is available. This may occu
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 lit simultaneously. This situation i
illustrated in Figure 3–2.
Figure 3–2: Mixed field integration
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.
Red Light Red Light Red Light Green Light
Red Light Red Light Red/Green Light Green Light
3–4 SpeedDome Ultra VII Operator's Manual