Understanding How Advanced Shutter Settings Improve Low-Light Performance - Siemens CCDA1415-DN Instruction Manual

9.5.1 Understanding How Advanced Shutter Settings Improve Low-Light
Performance
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Red Light
Siemens Building Technologies
Fire & Security Products
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.
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Fig. 24 Graphical view of Shutter Limit settings
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 traffic light changes from red to green in the middle of the field integration
interval (125 ms), you may get the impression that both the red and the green
lights light up simultaneously. This situation is illustrated in Fig. 25.
Red Light
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Fig. 25 Mixed field integration
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.
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Red/Green Light
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Configuring Camera Features
G r e e n L ig h t
Green Light
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BE_CCDA1415-DN.doc
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05.2004