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One word sums up the future of CCTV, and that's 'digital'. Digital technology is now making an impression in all areas and at all levels of video surveillance and security, yet its full impact has yet to be felt at this very early stage of the proceedings. But what exactly does digital mean, and what benefits will it bring?


Until comparatively recently CCTV and video in the wider sense has been an entirely analogue-based technology. That basically means from the camera to the display, visual information is represented by signals that vary in amplitude, or frequency, or both. Digital technology, by contrast deals with information in the form of numbers, at the simplest level a single binary digit or 'bit', represented by a 1 or 0. Digital systems are precise and the information they process is largely uncorruptable, moreover digital circuits are less affected by noise or interference and with the economies of scale brought about by the microchip and computer revolutions, much cheaper to produce than their analogue counterparts. 


Digital technology hasn't happened overnight, in fact digital circuits and circuit elements have been slowly permeating into CCTV systems for at least the last ten years, longer if you include ancillary items, like switchers and character generators. However, it began in earnest with the changeover from picture tubes to solid-state CCD image sensors. They utilise digital processing to create an (analogue) image from the grid-like matrix of picture elements or pixels. Shortly afterwards digital circuits began to be used in camera exposure and control systems. Digital circuitry is more flexible and can react much faster than an analogue equivalent, using so-called 'fuzzy logic', to emulate more human responses to changing conditions. It's also more consistent, an important factor for manufacturers and end-users. Digital circuitry has also been responsible for simpler installation and alignment procedures, less demanding maintenance routines, and a general all-round improvement in reliability.


More recently it has led to improvements in the performance of colour cameras, simplifying their construction and the consequent reduction in price. It has enabled new facilities to be added to cameras, including high-speed shutters, automatic white balance adjustment and more efficient exposure systems, but we're still only scratching at the surface of what lies ahead



Imaging is only the beginning, the most exciting developments lie in storage, image processing, analysis and system control. The end is now in sight for analogue video tape recording. Digital video recording technologies, relevant to the security and surveillance industry, now exist in prototype or pre-production form in other sectors of the video market. The first DVC (digital video cassette) VCRs, billed as the replacement for VHS, are expected to arrive in 1995, they will use Betamax sized cassettes giving up to four hour recording times at normal (real time) speeds, and, it has been suggested, between 500 to 700 hours in a time-lapse mode.


Initially DVC video recorder resolution should be equal to or better than Super VHS, more in line with the capabilities of modern cameras and significantly better than current VHS-based VTRs. However, the system is effectively open-ended and already work is underway on broadcast quality and high-definition versions, using the same tape format. In the short term the most important advantages will be no-loss copying from original recordings and the potential for direct data input to image analysis equipment. Current processing and enhancement systems depend on a potentially damaging analogue to digital conversion process which can result in the loss of important detail. With digital recording systems the data remains in its original  state and theoretically, at least, a DVC machine could be plugged directly into the back of a computer. The only possible drawback, in the early years at least, is likely to be cost, though there's every reason to suppose it will fall quickly once a domestic market for digital VCRs has been established, and that could take at least five years or until the end of the decade.



Tape is only part of the story, though, disc-based digital video recording systems now exist and promise to bring with them a range of new facilities. There are at least two technologies to keep an eye on; the first is a close relative of the compact disc or CD. Several versions of the magneto-optical (MO) re-recordable laser disc have been developed, the most promising by Sony who have already marketed an audio recording system under the name Mini Disc. Sony have produced professional and industrial MO recorders that are able to record video data. Disc-based recording systems have numerous advantages over analogue tape, including faster access times, durability and like DVC, compatibility with computer based analysis and control systems.


Other systems now on the market utilise the magnetic hard-disc storage systems used in computers, but like magneto optical discs several problems have still to be overcome. The biggest one concerns the massive amount of data involved in a video signal, equivalent to around 27 megabytes of information each second on a moving colour picture. The development that could turn an ordinary office PC into a viable video storage system is data compression. The two most successful systems are known as MPEG (motion picture experts group) and JPEG (joint photographic experts group). Both reduce the amount of data involved by comparing each frame of video with adjacent frames, working out which parts of the picture have been repeated -- background and sky etc. -- and only recording new information, such as movement.


Compression ratios of up to 200:1 are possible, though in order to maintain picture quality and resolution within acceptable limits for evidential purposes compression ratios of 15:1 to 20:1 are more practical at the moment. This would enable a one gigabyte hard disc, or 650 megabyte MO disc to record several minutes worth of real-time video, or many hours of time-lapse video. Storage times are at present insufficient for demanding CCTV applications, however this is another open-ended technology and we're seeing quite dramatic improvements in picture quality and compression all the time.


Once a video image is in the digital domain -- irrespective of how it got there -- it can be manipulated in an almost limitless number of ways, and this could have even more far-reaching implication for the security and surveillance industry. Clearly one of the most important developments is enhancement, whereby important detail can be extracted. Recent highly-publicised criminal cases, including the James Bulger murder, and Abbie Humphries kidnapping, where enhanced images taken from surveillance video recordings show some of the potential and proved pivotal in the police investigation and eventual outcome. Present enhancement systems can be expensive and cumbersome, but there's every reason to suppose that as computers become cheaper and more powerful it will become available as an on-site option, even in low-cost installations.


Taking these developments to their logical conclusion there's no reason why all of these technologies, including video storage, with image processing, analysis and control software shouldn't be integrated together in a single PC.



So much for the future, but what about the here and now? Digital technology lies behind numerous small but significant advances across the industry, here are just a few representative examples. Panasonic have recently introduced a PC interface, compatible with their System 300 telemetry; it will allow cameras to be remotely controlled over an almost unlimited distances, using telephone lines, fibre optic cables or microwave links. Miniaturisation is another key benefit of digital microcircuits, used for control and signal processing, and it has led directly to two other Panasonic products, the tiny GP-US502 3-CCD micro camera and the compact AG-6124 24-hour time-lapse VCR.


Sony bill the recently-launched SSC-DC30P as their first digital camera, it incorporates a feature called 'smart control' and amongst other things, carries out automatic backlight compensation, white balance adjustments and exposure/shutter speed according to the prevailing conditions. Sony are also rumoured to be working on digital video recording systems for surveillance applications, so watch this space!


On a slightly more down to earth scale Norbain's Vista Protos cameras utilise digital control systems, accessed via simple DIP switches, to preset adjustments for shutter speed, gain and backlight compensation. Digital circuitry is also behind  their new MA15Q 15-inch black and white monitor with built-in, real-time quad switcher featuring a test-card generator (for unused inputs) and quadrant zoom on VCR playback.


JVC's BR-S925 S-VHS time-lapse VCR uses digital technology in a number of important ways, including an on-board frame store memory with quad-screen display. This enables the outputs of up to 16 cameras to be recorded, and 4 camera images can be replayed sequentially. It also features an RS232 interface for external control and triggering.


Philips call the LDH-805 their 'thinking' camera, it's their most recent top of the line camera, designed for 24 hour surveillance in difficult conditions. It has the capability to change from monochrome to colour operation and features enhanced low light operation using a switchable infra-red filter. Digital fuzzy-logic circuitry makes informed decisions regarding exposure control, including compensating for bright reflections from moving objects, an important consideration in busy town-centre locations.


Finally to Mitsubishi who incidentally pioneered digital video recording over two years ago with their revolutionary DX-2000 DAT image recorder. This machine can record over 1100 colour images or 1800 monochrome images on digital audio tape (DAT) cassettes with a resolution of over 470 lines. Mitsubishi's range of video printers, including the new CP15B which has 321 dpi resolution is entirely dependant on digital technology. In addition to contributing to near-photographic image quality, digital circuitry is used in the analogue to digital conversion process, image capture, processing and control.



( R.Maybury 1994 1907



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