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Video Surveillance Turns the Corner-PART II
October 5, 2009
Any surveillance system starts with the cameras, which must have adequate resolution for human operators or analytical software to pick out vital information, such as license plate numbers. They must also be able to capture the entire scene you want to monitor, either by moving around or by having a stationary wide-angle — and typically high-resolution — view.
There are two main choices: high-resolution, fixed-position digital cameras or pan/tilt/zoom cameras. High-resolution fixed cameras could come to dominate the market because they can do digitally what PTZ cameras can only do by physically moving. According to a recent Frost and Sullivan analysis, even though a well-placed high-resolution digital camera costs more, it can do the job of several PTZ units at a lower overall cost.
Choosing the right lens is a discipline all its own. You have to make sure you have got the right lens with the right camera to get the images you are looking to visualize. Also, camera resolutions control network decisions; if you have a normal MPEG-4 stream coming off a camera — non-megapixel, VGA resolution, 30 frames per second — it is probably going to be 2 to 3 megabits/sec for that stream. If you have 3 megapixels, it could be as high as 40 megabits/sec. You really need to have a large, gigabit-type network to handle multimegapixel cameras, and you need to send that full image across.
To reduce traffic, you can put a DVR — or the IP equivalent, a network video recorder — on the edge of a network, or you can choose to record only when certain alarms are activated, Hughes said.
Wireless networks are starting to replace wired ones, particularly outdoors. But anyone considering them should be aware of the trade-offs in image quality, which is crucial in analytics. In wireless, there are always constraints about the bandwidth you can use; it is very important to balance the video quality with the bandwidth that you have.
Experts agree that the biggest hardware trend in video surveillance is H.264, a standard for a type of MPEG-4 format that enables more compact transmission and storage of video. In addition, an extension of H.264 and MPEG-4 called scalable video coding can improve video network scalability by varying the frame rate and resolutions of substreams in each video bitstream coming over the wire, depending on quality requirements. For example, a surveillance camera that only needs to capture seven frames per second at low resolution can share a line with a camera that captures high-resolution, full-motion video at 30 frames per second. Another emerging video standard, MPEG-7, allows more metadata tagging of videos, which improves searchability.
One area that cries out for interoperability is the link between network video devices and services, including video-management systems, analytics and PTZ cameras. Nilsson said a group started by Axis, Bosch and Sony, called the Open Network Video Interface Forum, hopes to publish a final standard later this year, when the first products will likely hit the market. He added that a new version of the power-over-Ethernet standard — 802.3at — will become the recommended power source for PTZ cameras, eliminating the need for separate power supplies.
High-definition TV surveillance is also starting to take off. All those technology trends add up to higher resolutions and faster frame rates on cheaper, more portable hardware. And they mean more realistic video and smarter, computer-assisted surveillance.
By David Essex
(Some content edited by this blog)