Selecting the display device for a video surveillance system may seem like one of the easier aspects in designing a video surveillance system, but giving short shrift to this essential component can have repercussions that can haunt an entire installation. In fact, that ubiquitous piece of hardware can adversely affect the images from the most expensive, high resolution cameras by making them look like something from a Webcam or render video from the most technically advanced recorders to look like a third generation duplication of a VHS tape.
Spending the extra money for a quality display is a smart investment. My experience has shown that when a customer cuts corners on display quality they regret it in the long run. Further, unlike most other hardware, displays have a longer path to obsolescence so the initial investment often results in lower total cost of ownership.
So why is it then that customers continue to accept, and dealers continue to offer, displays for very expensive and sophisticated video surveillance systems based on price or size? While the question is rhetorical, perhaps one of the reasons is the lack of understanding and appreciation of what a good display can add to a system.
In the Control RoomThere are several choices available for control room display technology, and probably one of the most popular today are liquid crystal displays (LCDs). Now available in sizes up to 65 inches, LCDs have been around since the 1970s and have a distinct head start over other flat-screen technologies. Their merits for use in a video surveillance application are many and include good color reproduction and brightness. To take advantage of megapixel camera technology, LCDs deliver resolution as high as 1080p and when POS (point of sale) systems are integrated with the system, LCDs display sharp data at native resolution.
The 65 inch unit aside, LCDs are relatively light weight, silent with no moving parts or fans, very thin and offer flexible mounting options. Additionally, the diagonal measurement of an LCD is the same as the viewable area, so there’s minimal loss of image area behind the display’s faceplate.
An LCD display consists of an array of liquid crystals that can be manipulated to either pass or block light and use very little power to display images. This basic design concept is common to all LCDs, ranging from simple calculators to color LCD televisions. However, because of this dependence on a backlight or ambient light for viewing characteristics, LCD viewing angles are limited and need to be taken into consideration when designing the control room layout.
Another flat panel display technology gaining in popularity for the control room is the plasma screen because of the excellent color reproduction and the truer black levels. Additionally, there is more detail in the darker areas of the picture which provide a greater subtlety of the image being displayed. It doesn’t take much explanation to demonstrate the importance of color and detail quality in a surveillance system.
Eye AppealIt’s also been said that plasmas generate more natural colors and an easier-on-the-eye picture than the stark brightness of a uniformly backlit LCD. Plasma screen pixels are turned off when they’re not being used and this contrast between the lit and unlit pixels makes the images appear sharp and more saturated. This switching from active to inactive is done more quickly than with an LCD and the faster switching results in fewer motion artifacts such as blurring or smear.
Plasma screens do however have a reputation for being more susceptible to screen burn in and although the newer plasmas are much better in this respect, the technology is still subject to this condition. It also has to power hundreds of electrodes to stimulate phosphors, hence the extra power consumption. In terms of viewing angles, the plasma screens have a viewing angle of about 160 degrees but care should be taken when hanging/locating any plasma because of its weight and fragility.
Finally, the CRT (cathode ray tube) display, whether the direct view model or the rear projection model, is probably the best choice in terms of high resolution, extended gray scale range and the ability to show motion without any artifacts. CRTs are generally priced lower than the comparably sized plasmas or LCDs because it is a mature technology.
Life Still in CRTThe “mature” technology label is a double-edged sword, however, for the CRT. While a few manufacturers as well as several integrators have discontinued production and/or use of the CRT, the technology and market have not disappeared quite yet and new designs are being produced in this field. Slimmer models with small screen sizes (up to 29 inches) are available to compete with the LCDs at a much lower price.
There are several new technologies on the horizon and one of the more interesting is organic light-emitting diodes (OLED). Wikipedia has an excellent explanation of the technology and a fun list of OLED’s advantages, including new applications such as roll up displays and displays embedded in clothing.
Regardless of which display technology you decide upon, be prepared to accept a few compromises. Look for ample and accessible controls for image adjustment and correction. Finally, remember that display settings drift over a period of time and need to be adjusted occasionally.