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Monitor fatigue 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.


Time-lapse 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 are used



Image useability 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.


The first 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.


The earliest 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.



The vast 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.



Looking a 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.



Not 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 for 1350.


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.


Mitsubishi's 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 respectively. 


Panasonic's 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.


The camera 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.


Dedicated 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.


Panasonic have 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



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