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By Charles Evett

(Photo by Winsted Ltd.)

In case we forget the sheer pace of change within control rooms, it was little more than ten years ago that many CCTV surveillance systems still used mono (black and white) cameras, while their owners/operators continued to evaluate the cost/benefit ratio of switching to color images.  Nowadays, similar assessments are being made by an increasing number of control room managers about whether to retain long familiar Cathode Ray Tube (CRT) displays and monitor walls.

Several factors are driving this shake-up in traditional thinking, starting firstly with technical advances in display technologies, which now deliver improved images using space-saving flat-screen spot monitors at a sufficiently low price to make the switch cost-effective.  But more fundamentally, from an operational standpoint, older cathode ray tube displays no longer allow operators to adequately display increasing amounts of computer data overlays onto video --  an effect that can be liked to an “electronic piece of paper.”

CRT Remains Popular

The security and safety advantages offered by this enhanced data functionality cannot be exploited by the in-built restrictions of older format display monitors such as CRT.  Nevertheless, it must be stated that CRT remains the surveillance sector’s technology of choice, given the high screen resolution it provides for video applications compared with digital alternatives.  In addition to this superior image performance, it also offers the advantage of comparatively lower cost.

However, these traditional monitors are constricting control rooms by failing to adapt to evolving types of information and changing demands on operators -- for instance, in handling reactive data alerts from lone worker protection systems.

One example of the opportunities on offer is the chance to display maps of the surveillance coverage area with camera positions marked, which can then be combined with other information such as GPS tracking of vehicles -- with all of this data being interactively meshed with live and recorded picture feeds from CCTV and IP cameras.  By comparison, existing banks of CRT monitors do not even allow operators to alter the display format of text and pictures from fixed image sizes and are therefore an inflexible response to the utility value that can be extracted from this technology.

Display Screen Alternatives

So what are these display screen alternatives?  How proven are they?  Is anyone using them yet and do the costs involved make economic sense?  Positive responses to these questions can be seen, firstly, in the ability to deploy an effectively seamless digital display that isn’t damaged by the very images it handles, while providing screen sizes that can be custom made to fit each control room environment exactly.  The processors behind the various types of digital display now available can additionally handle any number and size of images, enabling operators to share valuable incoming information.  These displays reduce operator fatigue, as they are easier to work with, while managers wishing to continue using their existing video matrices can easily replicate their monitor wall.

(Photo by Winsted Ltd.)

The first moves toward this digital future have already been seen in the increasingly prevalent use within control rooms of a large central display screen, surrounded by conventional size CRT monitors.  Some users are now taking their constructive experience of this display configuration a step further.  The results are being seen in terms of fully dynamic displays, using emergent technologies such as LCD and rear-projection cube screens.  Larger digital screens in turn allow for larger images that provide operators with overviews of scenes -- the detail of which can either be shared as a single camera feed on the main display, or pulled up by individual operators when required in the familiar way, using a spot monitor positioned conveniently on the console in front of them.  In essence, therefore, this approach allows the creation of an intelligent closed-loop system.

CRT Vs. Plasma

Comparing common cathode ray tube monitors with flat-screen plasma displays, the advantages of CRT include their high resolution and brightness capabilities, the different screen sizes available and their relatively cheap cost because of the large production volumes involved.  Against this, there are downsides such as the use by this technology of phosphor, which means that any image left on-screen for a sustained period will produce image ‘burning’-- an effect that’s particularly noticeable, for instance, when moving from a quad display to a single frame image.  CRT displays also require new tubes after around 8000 hours’s use.

Plasma technology works on a similar principle to CRT, in terms of ‘exciting’ phosphor in order to produce the image, so similar image retention effects can occur unless the scene is regularly refreshed.  But plasma does offer benefits including a small “form factor” allowing 40 inch+ size screens to be wall mounted, as well as volume production that has driven prices down.  However, the comparatively large mullions of plasma screen casings make it very difficult to arrange a number of them together as a screen array because of the physical interruptions caused by the casings.  Plasma displays also only have an average effective lifetime of between 10,000 and 20,000 hours, though some manufacturers now offer “double phosphor” alternatives to double this.

Plasma Vs. LCD

The comparative advantages of LCD mean plasma screen production is now coming to an end.  For, by comparison, liquid crystal displays do not suffer as badly from image burning and have a long lamp life -- typically around 50,000 hours.  A 24-hour operational control room can therefore count on several years’ use from an LCD screen.

Other upsides to LCD include their small depth, though like plasma they do have relatively large casing mullions.  LCD also used to have a problem with response time to fast motion images and graphics, which tended to smear across the screen, though this has been adequately addressed more recently in the professional LCD monitors being sold.

Screen sizes of around 40 inches are the most common, though larger LCD displays are occasionally used.  Moving up in terms of scale, to screens of between 50-300 inches, or even 1m by 3m wide, use can be made of either front or rear LCD projectors -- often deployed in company board rooms for presentations, etc.  However, a typical rear projection unit is designed around an active matrix system, which has a relatively low lamp life of between 1,000 and 2,000 hours, meaning it would have to be changed 4-8 times annually.  Moreover, as a transmissive technology, there are other concerns over issues such as heat generation, hot-spotting and colour rendition.  LCD projectors aren’t therefore generally suitable for control rooms.

Meanwhile, reflective LCD has also sometimes been used to achieve high-resolution display images.  Compared with transmissive LCD technology, which is typically pixellated, reflective screens produce a smoother image.  However, the color reproduction of these displays does change over time, while heat management issues must also be addressed -- drawbacks which have led to this technology being overtaken by more effective and efficient alternatives.

DLP Gains

The technology with major benefits for control room environments is Digital Light Processing, manufactured by Texas Instruments.  Using tiny digital micro-mirror devices, which physically move by ±12°C, different screen resolutions can be produced -- for example, a control room might choose an XGA resolution using 1024 x 768 mirrors.  DLP reliability is high ? it’s designed with an MBTF of 120,000 hours -- while the mirrors’ range of motion provides a broad range of image grades from white through to black, which in turn provides far greater color accuracy and image rendition than is available using an LCD screen.

DLP screens also provide linear imagery, i.e., when a number of them are combined one single display can be created (eg using video wall cubes), with the added benefit of uniform colour images throughout.  Additionally, the technology can run 24 hours a day without risking damage to the display -- a benefit proved over the eight years DLP has been in use.

Cost Comparisons

Ongoing DLP costs are low too, since the system’s lamp is the only component requiring annual replacement (for approx. ￡400/US$700).  DLP is more expensive than other technologies, though capital and running costs should be considered over a control room’s lifespan.  Whilst a 40-inch LCD screen has a list price as low as ￡2,000 (US$3,400), a 50-inch rear-projection DLP cube would cost some ￡9,500/US$16,000.

To conclude, the data resources now becoming available are driving the market, in terms of computer generated applications.  Digital displays can bridge the old and new by allowing control room operators to continue viewing analogue video inputs through matrices, while simultaneously integrating these with local area networks.  In short, the “electronic piece of paper” display that was just waiting for these applications to arrive is now a realistic and cost-effective reality.

Charles Evett is CEO of Lund Halsey Consoles  (www.winsted.com).

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