Q+A CENTER

PCs today are increasingly used in conjunction with video management software to record video feeds from network cameras. However, this form of centralized processing represents a bottleneck and generates a substantial network load. This is because images have to be transmitted to the central PC for evaluation, even when no events are captured. By contrast, new "smart" network camera systems with integrated PCs reduce the network load to practically nothing, and there is no limit on the number of these cameras that can be connected to a network.

Network Cameras On The Ascent

Instead of analog video cables, network cameras use TCP/IP — a standard commonly found in IT network technology — to transmit images. This gives them several advantages:

• Affordable, universal image transmission: All kinds of network technology — including WLAN, DSL, ISDN, GSM and Ethernet — can be used to transmit the cameras' images inexpensively. Special analog cabling is not needed. Using leased lines or the Internet, the cameras can be accessed from anywhere in the world. And because there is no need to comply with rigid analog video standards, there are no longer any restrictions on image resolution. This means that the first megapixel security cameras are now available.
• License-free Web technology: Access to the images and recordings is Web-based using browser software available on any PC (for example, Internet Explorer or Netscape). Regardless of the operating system used and the number of users viewing images from the cameras, there are no license charges for software or maintenance.
• High security: In contrast to analog video cable, which can be tapped electromagnetically using just simple equipment, network cameras can be protected in a variety of ways, including software encryption with well-known technologies like PGP (Pretty Good Privacy) or secured VPN (Virtual Private Networks) routers over the Internet.
• Unlimited expandability: Large companies typically run hundreds of PCs, networked worldwide, that keep their data on company servers. Hundreds of cameras can be networked in exactly the same way. This kind of network structure is easy to expand — using WLAN technology instead of cables, if necessary.

Change of Scenery

As a rule, simple live monitoring is not sufficient in video surveillance. When used for evidence recording or in situations requiring unattended monitoring, scenes must also be tape-recorded. To keep the costs of storage capacity low and to optimize searching through recorded material for events, usually only those sequences are recorded in which changes of scene or motion have been detected. These events do not need to be just recorded, they may need to trigger an alarm as well.

Recording all the important scenes and avoiding unnecessary recordings calls for scene change detection (video motion detection); here, video sensor systems play an important role. Because of the need to document the scene prior to an event or incident (pre-alarm), the recording system also has to be equipped with a circular buffer capable of storing a few seconds of video.