Quality control: Enhancing images with video scalers
Feb 1, 2002 12:00 PM
By JOHN LOPINTO
With heightened security needed in high-traffic areas such as airports, parking lots and building egresses, existing surveillance techniques need to be reevaluated at all levels. The addition of more cameras and tighter monitoring practices should be considered, as should improving the quality of viewable images.
A solution to enhance the quality of video images is to use a video scaler. Video scalers have long been used by home theater enthusiasts who desire video images with a film-like quality. Video scalers can also be found anywhere crisp, high-resolution images are desired.
Using video scalers for security applications is a relatively new concept, but one that provides substantial benefits. Taking images captured by standard CCTV cameras and processing them in a way that makes it easier for security personnel to spot and analyze subtle, suspicious details can improve the overall effectiveness of any security operation.
HOW DO VIDEO SCALERS WORK?
Video scalers are designed to take standard television video, such as that captured by CCTV cameras, and manipulate it in a variety of ways so that it becomes consistent with standards used by higher-resolution display devices, such as CRT and LCD computer monitors, data projectors and new HDTV plasma displays. At the most basic level, scalers (as well as their technological predecessors ¡ª line doublers and quadruplers) convert the interlaced format of standard TV video into a non-interlaced, or progressive scan format. This means that the odd and even lines of the video image, which are "painted onto the screen" in separate passes when displayed on a standard TV, are combined into a single frame by the scaler. The resulting image, in which all lines are "painted" in a single pass by the display, has none of the flicker inherent in the original TV video.
Video scalers also perform the important function of "scaling," or resizing the resolution of the video image so that it matches the resolutions used by today's high-resolution displays. This involves analyzing the 480 visible lines present in the original video signal, digitally sampling them, and then through a process of sophisticated interpolation, calculating how this visual information should be displayed in a picture containing additional horizontal lines. A low-cost, high-quality scaler can output an image with as many as 1024 lines. Such a scaled image, with nearly three times the vertical resolution of the original video, provides a picture in which small details appear more defined.
It is important to note that while a video scaler facilitates the viewing of TV video in a higher-resolution format, no additional detail has actually been captured by the camera. So, the scaler's output must be seen as a tool to enhance the viewing and monitoring experience of security personnel but not as a means to actually capture and record additional information. It is a tool to allow security personnel to perceive more detail when viewing surveillance video.
INTEGRATING VIDEO SCALERS INTO A CCTV SYSTEM
Video scalers can be used in a variety of ways within a monitoring system. One option is to use the scaler in a "real-time" monitoring scenario, such as the one illustrated in Figure 2. In this case, feed from a CCTV camera is transmitted to a video scaler located at a monitoring station. The scaler processes the image in real-time and then outputs it for display on a high-resolution monitor located at the viewing station. Note that, from a practical standpoint, the scaler should be located in close proximity to the viewing monitor rather than near the CCTV camera. This is because transmitting the high-resolution output from a video scaler requires more bandwidth than transmitting a standard TV video signal. Therefore, the signal traveling the extended distance between camera and monitoring station should be in original TV video format.
A variation on this real-time application is to use a scaler in combination with an image multiplexer, or "quad." Video from four CCTV cameras are fed to the multiplexer, which combines them into a single TV image with each image displayed on one quarter of the screen. The output from the multiplexer is then directed to a video scaler, which outputs it to a higher resolution image for display on a PC monitor or projector.
Another option is to use a video scaler for viewing archived material (Figure 1). Video stored on tape or DVR can be fed to a video scaler and then output to a high-resolution display device. This might be particularly useful in situations where teams of security professionals need to view recorded video together in a collaborative manner. For example, displaying scaled output on a data projector in a theater environment would allow a security team to review suspicious footage on a very large screen with near film-like image quality. Previously overlooked visual details might become apparent in this type of set-up.
A third option is to design an installation that combines both examples. In Figure 3, the video from a camera is fed to a video distribution amplifier, which splits it into two separate, identical signals. One output from the amplifier is fed to a VCR for archiving purposes. The other is fed to a video switch, which passes the signal on to a scaler, providing scaled output in real-time.
In addition, output from another VCR is also fed to the video switch. Such a set-up enables the monitoring station to be used either for viewing the real-time camera feed or to switch to prerecorded videotape. Because two VCRs are employed, the VCR unit dedicated for recording can continue to record live feed from the camera even if the scaler is outputting pre-recorded video from the other VCR. As an alternative to this arrangement, a video scaler with multiple inputs and built-in switching capabilities may be used, thus eliminating the need for a free-standing video switch.
John Lopinto is president, CEO and co-founder of Communications Specialties Inc., a Hauppage, N.Y.-based supplier of computer video technology. For information, e-mail firstname.lastname@example.org.