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
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
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
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
( R.Maybury 1994 1907