hasn't quite made it into the medical text-books, but it is a recognised
condition that can dull the senses of an otherwise vigilant security operative,
rendering many thousands of pounds worth of video surveillance equipment
useless. Staring at unchanging monitor screens can have a semi-hypnotic effect,
and sooner or later the eye and brain seeks distraction, possibly causing the
operator to miss a potentially important incident.
This problem is
inherent with permanently manned video surveillance systems; fortunately there
are ways to alleviate the mind-numbing effects of monitor fatigue, or remove
them all together and at the same time increase the effectiveness of a system.
The best solution would be to eliminate the human factor altogether, though,
despite the best efforts of electronic hardware and software engineers there is
still no real alternative to an alert, analytical eye, but it is possible to
make more efficient use of an operatives skills, with the appropriate technology.
The two devices
which have had the most far-reaching impact on video surveillance, are
time-lapse video recorders and camera switchers. When combined with various
types of sensors, processors or external alarm triggers there is no longer any
need for constant observation, in most types of installation, human
intervention is normally only required when the system detects an anomaly or
attention is called to an event.
video recorders have become core-components in video surveillance, not only for
the purposes of unattended surveillance operation, but as an inexpensive
activity log in situations where actions, processes or events need to be
analysed. Time-lapse VCRs have altered comparatively little in the past ten
years though picture quality has been steadily improving and prices have fallen
appreciably. In contrast camera switcher technology has already undergone some
major changes recently, and this has had a profound effect on the way that they
THE RIGHT IMAGE
is always a prime concern for both installers and end-users and this is an area
where both VCRs and switchers have had a significant impact. Aside from
on-going improvements in video camera performance and VCR replay facilities one
of the most important developments has been asynchronous processing, used on
the new generation of camera switchers. In a nutshell it enables the outputs
from two or more cameras to be combined so that they can be simultaneously
monitored and recorded. The problem with a conventional sequential switcher and
time-lapse VCR set-up is that most of what is seen by each camera is missed. In
a four camera system, for example, only 25% of the total activity will actually
end up on tape as the switcher steps though each camera input in turn.
attempt to get around this problem was addressed by gen-lockable cameras and
time-division multiplex processing of four, nine or sixteen camera inputs, but
this is a costly and often temperamental technique that requires careful
installation and alignment. The breakthrough came in the mid-1980s with the
introduction of digital timebase correction systems which can be used with
conventional video cameras, and may even be retrofitted to existing
multi-camera systems. Timebase correction does away with the need for genlocked
cameras, instead the free-running video inputs pass through an analogue to
digital converter and are then read into field-store memories. The data can
then be clocked out so that after re-processing the images are in perfect
synchronisation with each other; this means they can be combined into various
multi-image display formats, for monitoring and recording. Digital processing
has a number of additional benefits; images may be frozen for detailed
analysis, and even magnified, though so-called electronic zooming normally
entails considerable loss of detail.
examples were only capable of processing monochrome images, increasingly newer designs can handle colour
inputs and some of the most recent quad systems now feature real-time outputs,
with the display clocked at 25 frames per second, so they can be recorded and
viewed on a VCR. Most switchers are, or should be transparent to the video
signals passing through them, so picture quality is not usually a major
consideration, the other components in the installation (i.e. cameras and
VTRs), ultimately dictate how well, or badly, the system performs.
majority of time-lapse video recorders use the VHS recording system. Most
machines are based to a greater or lesser extent on domestic VCRs and even
though many use uprated mechanics and purpose-designed electronics, performance
is comparable with their domestic counterparts, though even the best ones are
still only capable of resolving around 230 horizontal lines, or between one
third and a half of the information contained in the output from the video
camera, or viewable on a monitor screen.
One of the most
significant developments in the last eight years has been the introduction of
Super VHS time-lapse video recorders which can resolve up to 400-lines.
Unfortunately these machines do not represent an instant upgrade as S-VHS
system depends on cameras with Y/C formatted video outputs, and a
suitably-equipped monitor, with a Y/C video input, in order to view the
recorded and off-line images at maximum resolution. Moreover, any other device
in the video signal chain, including cabling and switchers, must also be Y/C
formatted otherwise any increase in resolution will be compromised; at the
moment Y/C switchers are very few and far between.
There are other
drawbacks too, compared with composite video systems, Y/C signals do not travel
well and cable lengths are limited. It also has to be said that only a small
proportion of cameras are fitted with Y/C outputs, and the ones that are tend
to be significantly more expensive. At this stage of their development Y/C
based systems are best suited to critical identification applications, rather
than gross area monitoring where the need for higher resolution is not usually
so great. The difficulty and expense in networking and switching signals means
it will remain that way for some time.
little further into the future a recent announcement by JVC in Japan of the
development of the W-VHS system could have implications for time-lapse
recording. W-VHS was originally developed as a recording medium for
high-definition video signals and it works by splitting the 1125-line picture
into two 525-line segments (lost lines are electronically re-processed). In
this manner W-VHS video recorders can also record two 525-lines pictures
simultaneously. Work is underway on a PAL/CCIR version which could record two
625-line signals. W-VHS, like S-VHS, is backwards compatible with standard VHS
and the first NTSC standard machines have recently gone on sale in Japan. Thus
far most of the development work has concentrated on domestic applications but
if the past experience is anything to go by improvements in home VCRs
frequently filter through to the surveillance industry.
surprisingly most of the main players in the time-lapse VCR market are also
leaders in domestic VCR technology, they are Hitachi, JVC, Mitsubishi, Panasonic and Sony. GYYR are one
of the exceptions, their highly advanced decks are based on Hitachi components,
their current machine is the TLC 1800X-S16MP-TDS; it's an advanced 960-hour
deck with a built in switcher for up to 16 cameras, it is presently selling for
£1995, various options are available with or without time/date search
facilities, and a 12volt DC power supply. A new model, designated S16MX with an
on-board digital multiplexer is due out shortly, the price has yet to be
decided. Hitachi have two VHS time-lapse decks in their range at the moment;
the VTR-1000 has a 24-hour recording mode with a built-in 4-way camera
switcher. It currently sells for around £790. Their other machine is the
VTR-2000, this has 11 recording speeds, up to a maximum of 720 hours, it sells
JVC also have
three machines, all with 960-hour recording capabilities, they are; BR9060E, a
standard VHS model costing £1275; the BRS920E, which is an S-VHS model, it is
priced at £1830, and the BRS925E, it also has an S-VHS recording system, this
time with a digital multiplexer, and it costs £2595.
line-up includes four machines, the first is the HS-5424E, a basic 24-hour VHS
deck priced at £750, next is the HS-5300E(B)A, a 960-hour VHS machine costing
£1425, the other two are the HSS-5600E and HSS-600EBRS, they're both S-VHS
models with 480-hour recording times, the main difference is that the 600EBRS
has an RS232 interface; prices for the two machines are £1800 and £2000
three models are the AG6024HB, this is a 24-hour VHS machine, selling for £675;
the AG6040E, which is also standard VHS but with a 480-hour recording mode, it
costs £1295, and the AG6730E Super VHS machine, 480-hour recording, and a price
tag of around £1895.
Sony have two
models, the SVT-100P, a 12/24-hour VHS model for £790, and the SVT-5000P,
another VHS machine but with a 960-hour capability, it costs £1200.
switcher market is far more diverse; there are literally scores of
manufacturers and products, and it is virtually impossible to compare like with
like. However, if we restrict ourselves to leading-edge quad and multiplex
switchers then it becomes a little more manageable. Robot are major innovators
in this area and they market three colour multiplexers, with four, nine and
sixteen asynchronous camera inputs. The prices for the three are: MV94 £1395
(4-camera); MV99 £2065 (9-camera) and £2925 for the MV96 (16-camera). Also
relevant to this market are the Robot MV45 and MV85 mono and colour quad
processor which sell for £575 and £1185.
Micros are one of the market leaders, they have a range of 8 and 16-camera
switchers. The 8-camera units are called Sprite, there's two models, the
monochrome version costs £750, whilst the colour model sells for £1675. Their
Uniplex range all have 16 camera inputs, Serie 1 is available in simplex or
duplex configurations for £1370 and £2490; Serie 2 models sell for £2265 for
the simplex model, and £3520 for the duplex version. Finally there's Duet, a
16-camera multiplex unit costing £2995. All of these switchers require a
keyboard unit, which sells for a further £175.
two quad units, the WJ-410 which is a monochrome unit, priced at £775, and the
WJ-450, which is a colour model, and sells for £1650. Sony have one quad unit,
it's the YS-Q400, a 4-camera model with an RRP of £2300.
R.Maybury 1994 0401