CCTV Overview
For decades closed-circuit television (CCTV) security systems were based on a standard developed by the National Television System Committee (NTSC) which restricted image resolutions to just 480 vertical scan lines. In other words, the image was created by scanning the scene top to bottom to produce 480 rows of data. As can be imagined, this seriously limited the image quality for large scenes, such as is typical for security surveillance.
A particularly troubling feature of the NTSC video standard was the use of an interlaced video scan. Interlacing is a double scan process in which “odd numbered” lines in the video field are drawn, or captured during the first scan, and the remaining “even numbered” lines, are drawn, or captured, during a second scan. This was original done to limit the appearance of “flicker” in the image as the television or monitor was refreshed. This is no longer necessary with current monitor technology. Although interlaced scanning yields greater image resolution for stationary subjects, it loses up to half of the resolution and introduces undesirable “combing” artifacts, when the subject is in motion. This can be crippling for a surveillance system.
Video Recording Devices
Security applications almost always require video imagery to be recorded over long periods of time and stored for retrieval. Until recently this was accomplished with standard video cassette recording devices. These methods required frequent changes of the tape cassettes, limited the ability to scan and retrieve video data at specific time points, and suffered from long term degradation of the signal recorded on magnetic tape media.
A considerable leap in performance was achieved with the introduction of low cost digital recording devices in the late 1990s. Both computer based and standalone, these devices enabled video signals from multiple cameras to be digitized and recorded to computer hard drives. This allowed hundreds of hours of video data to be recorded and stored, and most importantly, allowed random access to retrieve video segments at specific points in time, rather then running through an entire tape.
Despite the improvements introduced by digital recording devices, the basic limitation of standard, low resolution, video image quality went unchanged, even as low cost, high resolution, digital video cameras became available. This was because the link between video cameras and recording devices continued to be based on the old NTSC video standard and analog technology which did not support digital data or higher image resolutions.
IP Camera Development
Beginning around 2002, changes in industrial video technology, driven by the labor saving machine vision and robotic applications, produced a number of new digital image interface technologies, such as LVDS, Camera Link, and Firewire. All of these technologies supported high resolution, progressive scan, digital cameras. However, the shear bulk of the cables and limitations on cable length made them impractical for long distance installations typical of video surveillance applications.
This finally began to change as video data transmission over IP networks enabled the marriage of digital video recording devices and high resolution video cameras for security applications.
IP, or internet protocol, is a digital standard that has been used for decades to link networks of computers for transmitting large amounts of data. As the technology matured, the speed at which digital data could be transmitted brought it within range of that required for transmission of video imagery.
The development of IP compatible video cameras has brought the following advantages to the security surveillance industry:
- IP CCTV cameras can provide multi-megapixel resolution and HDTV image quality at 30 frames per second.
- IP cameras use a “Progressive” scan format, scanning the image top to bottom in a single frame, eliminating the combing effect described previously for the old NTSC interlaced video format.
- Cameras can be moved around anywhere on an IP network (including wireless).
- Video, audio, and pan/ tilt,/zoom functions may be transmitted via a single CAT5 network cable.
- Live video can be viewed from any computer, from any location, including over the internet and many mobile devices.
HD CCTV Systems
Of course, almost immediately, the parallel development occurring with High Definition TV in the consumer market was married to digital security cameras and the new IP interface for CCTV.
High-definition video, or HD video most commonly refers to devices with display resolutions of 1280×720 pixels (720p) or 1920×1080 pixels (1080i/1080p). definition video. HD security cameras cameras offer outstanding image quality at, or near, real time video rates, and a 16:9 widescreen format. With HDTV, video images show up crisp and clear, and are formatted for modern screens and monitors. HD CCTV cameras are ideal for surveillance applications where full frame rate and exceptional image quality are prioritized.
Summary
In just this past year a number of manufacturers have introduced IP CCTV cameras with HD formats for the security market. Manufacturers such as Toshiba, Sony, Panasonic, and Ganz, all carry a full line of high resolution, HD security cameras and IP accessories. Prices have fallen quickly and are competitive with the older technologies particularly when considering installation and maintenance costs, since most systems can use existing CAT5 IP networks.
If you are shopping for a new security system, there really is no reason not to consider an HD security camera system first.
Justin Martin writes about HD CCTV Camera Applications at http://BlueCoastImaging.com
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