Integration has become a standard requirement for video systems and ViconNet Rev 3.0 supports that need with integration to Hirsch and Lenel Card Access and ObjectVideo’s VEW Video Analytics System. For more information, visit www.vicon-cctv.com.
A Bridge from Analog to Digital Video
GE’s Security’s SymNet encoders/decoders allow connections of any existing analog cameras, domes, keyboards and monitors to an IP network. The encoder converts video from analog cameras into a MPEG-4 data stream of 2Mb/s. Decoders convert the MPEG-4 data stream back to composite NTSC output for viewing on traditional analog monitors. Two built-in serial ports on each unit let users communicate with PTZ cameras on the network using RS-232 or RS-485 protocol from a PC or keypad connected to an encoder. For more information, visit www.GESecurity.com.
Irrelevant and Immaterial
In North America and Japan, the NTSC standard (National Television System Committee) is the predominant analog video standard. In Europe the PAL standard (Phase Alternation by Line) is used. Both standards originate from the television industry.
NTSC has a resolution of 480 horizontal lines, and a frame rate of 30 fps. PAL has a higher resolution with 576 horizontal lines, but a lower frame rate of 25 fps. The total amount of information per second is the same in both standards.
When analog video is digitized, the maximum amount of pixels that can be created is based on the number of TV lines available to be digitized. In most analog security applications only a quarter of the analog picture is used, based on quads making 4 cameras share the maximum resolution. This quarter of the total image size has become known as CIF (Common Intermediate Format) in the video surveillance industry. In NTSC CIF means 352x240 pixels, and in PAL 352x288 pixels.
With the introduction of network cameras, CCTV has suddenly become 100% digital systems. This renders the limitations of NTSC and PAL irrelevant. Several new resolutions derived from the computer industry have been introduced, providing better flexibility. Moreover, they are worldwide standards.
Two different techniques are available to render the video: interlaced scanning and progressive scanning.
- Interlaced Scanning is a technique developed for CRT-based TV monitor displays. It is comprised of 576 visible horizontal lines across a standard TV screen. Interlacing divides these into odd and even lines and then alternately refreshes them at 30 frames per second.
- Progressive Scanning scans the entire picture line by line every sixteenth of a second. Computer monitors do not need interlace to show the picture on the screen. This technology eliminates flickering and improves image detail.
Camera Image Sensors
The image sensor transforms light into electrical signals. Two technologies used for camera image sensors are:
- CCD (Charged Coupled Device). CCD sensors were developed specifically for the camera industry and have been in use for over 20 years. Advantages of CCD include better light sensitivity than CMOS sensors, therefore better images in low light conditions. In extremely bright conditions, CCD images may smear or bleed.
- CMOS (Complementary Metal Oxide Semiconductor) sensors are based on standard technology already in use in computer memory chips. Most high quality cameras use CCD sensors but CMOS sensors are improving.
Recent advances in CMOS sensors bring them closer to their CCD counterparts in terms of image quality. However, CMOS sensors remain unsuitable for cameras where the highest possible image quality and smallest camera size are required.
Unlike traditional analog cameras, digital network cameras are equipped with the processing power not only to capture and present images, but also to digitally manage and compress them for network transport.
VGA is an abbreviation of Video Graphics Array, a graphics display system for PCs originally developed by IBM. The resolution is defined at 640x480 pixels, a very similar size to NTSC and PAL. The VGA resolution is normally better suited for network cameras since the video in most cases will be shown on computer screens, with resolutions in VGA or multiples of VGA. Quarter VGA (QVGA) with a resolution of 320x240 pixels is also a commonly used format, very similar in size to CIF.