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Another significant improvement in camera technology is the introduction of variable-speed camera positioning devices that provide both video signal transmission and remote control camera movement (pan-tilt) using a single coaxial cable, simplifying installation and reducing cost. Previously, a coaxial cable transmitted the video signal, and a separate set of conductors provided remote control of the camera's horizontal (pan) and vertical (tilt) movement.
Advancements in camera technology have also prompted the development of higher quality monitors both for live viewing and playback of recorded images. Large flat panel LCD screens are replacing the venerable CRT type display.
These screens are comprised of a single sheet of glass that uses primary colors to produce an extremely sharp display without the appearance of faint duplicate or secondary images (ghosts) associated with previous generation LCD screens.
The digital video recorder (DVR) has largely replaced the VCR in video surveillance applications and brings all the advantages of digital signal processing to the process of recording, storing, transmitting and reviewing of video images.
Recording digitally is done either with a dedicated box or with PCs equipped with video capture cards. Which type you use will depend on the particular application, and your level of expertise.
Replacement of the VCR as a key component in a video surveillance system not only eliminates the purchase, changing, cataloging, and storage problems associated with VHS tapes, but also provides a major upgrade in the overall quality of video recording.
A DVR is a computer that digitally records and stores the visual images transmitted from the video surveillance cameras linked to it. The DVR shares the same data compression technology as a computer, enhancing the amount of information it can save for future use.
The amount of actual storage space depends on the size of the unit's disk drive, which may range from 80 GB (1 gigabyte is equal to 1024 megabytes) to 1 TB (1 terabyte is equal to 1024 gigabytes).
“Unlimited” storage is achievable through the use of redundant arrays of independent disks (RAID) server. With this option, recorded images can be partitioned over several different disk storage drives. Similarly multiple DVRs can be linked over a network, to support, view and record an unlimited number of cameras at an unlimited number of locations.
The advantages of using a DVR instead of the traditional VCR are numerous. Unlike VHS tapes, which lose picture quality when reused and recorded over on several occasions, digital images recorded by the DVR never degrade. Instead, they maintain a crisp, sharp presentation, regardless of the number of times they're played or reviewed.
Additionally, problems associated with videotape stretching, tearing, or breaking due to repeated use are avoided. Digital images recorded by a DVR are stored by both date and time and can be easily recalled for playback, while the search for a specific recorded event associated with a VCR is very time consuming. Both the PC-based and embedded operating system styles of digital video recorders provide functions usually related to computer networks, including remote recording, viewing, and playback without compromising image quality during the transfer and receipt of video images.
Another feature associated with DVRs is their ability to record at higher frame rates than those associated with a VCR, providing enhanced visual quality and image definition. At 30 frames per second, the DVR captures events in the same manner as the human eye sees and processes information, which led to the term “real-time” video.
Multiple channel DVRs offer functions previously associated with separate system components, such as a matrix switcher or a multiplexer.
DVRs and video servers typically provide the ability to record multiple cameras individually, as well as simultaneously view prerecorded video from selected cameras over multiple monitors from multiple locations.
Although the term digital is used liberally in video, there are several aspects to a video system which may not fill the strict definition. Although virtually all cameras use digital imaging, not all cameras transmit the image to the system digitally. The legacy transmission system is coaxial cable which is considered analog. Other cameras use UTP (unshielded twisted pair) wire to transmit the image. IP cameras are network devices which transmit images digitally to the head-end of the respective system.
SPECO’s DVRs are representative of the new breed of cost-effective digital video processing devices which are redefining video surveillance and security.
Digital video delivers improved quality, which enables more details and changes in images.