When it comes to choosing a monitor for a Surveillance Camera System, people may think that all screens are the same. Far from that. The size of the screen is a variable that must be selected, depending on the use, on the distance for viewing and on the comfort one wish to enjoy. If multiple cameras have to be serviced, one could obviously dedicate one monitor to each camera. Usually however one of the two following different solutions may be adopted. One can split the view on the monitor among the different cameras, using a device called multiplexer, dedicating to each camera only a small part of the screen. This way one can always have an overall view of all the cameras, and one can select each one of the pictures for full screen display, hiding the rest. Alternatively one can employ a different device called a switcher, which will show on the full screen the view from each camera in turn, according to a predetermined schedule, assigning only a fraction of the time to each camera view. Here too a camera can be singled out for continuous viewing. The camera and the monitor must be compatible, that is they must speak the same language. That means that those components must be either both monochrome (black and white) or both built for color viewing and reproducing. What is really needed? A monochrome or black and white monitor can only display different shades of gray but resolution and definition are generally greater thanks to a larger number of lines being scanned to reproduce the picture. Furthermore in case of low light, a B&W monitor can still provide sufficient information, whereas a color device would need more light to show a useful image. But that is only part of the dilemma. Television systems are based on conventions or protocols that establish how a signal is generated, transmitted and reproduced. Camera and monitor will work together for taking images and for viewing them, provided both are of the same standard (NTSC, PAL or SECAM). An unused TV set having a connection for Video In, will generally be usable as a monitor if of the same standard as the camera, although it will usually provide a lower quality picture than a dedicated monitor. In the majority of cases the Surveillance Camera produces an analog video signal that is transmitted to the device for reconstructing the image. The color monitor is capable of reproducing a color image, due to the three basic color phosphors (red, green and blue or RGB) that form each pixel or picture element. What about using a computer screen? That is a completely different device. In order to be reproduced on a PC screen, the analog signal of the camera must be digitized, that is transformed in a set of data corresponding to each picture element (pixel) of the screen. This function is performed by a video grabber or video card. That is the primary difference between computer screens and television monitors. |
