Multiplexers: Once again, the multiplexer must take the NTSC image from the VCR, convert it to pixels, process it, then convert it back to NTSC for the monitor.

Monitor: monitors take the NTSC input and display it on a large vacuum tube.

Cables: Don't forget cables. Each time the NTSC image is moved from one device to another, it typically is transported through coax cable. Each cable has a connector at each end. If you have made one of these connections, you know why bad cables are the number one cause of failures in the CCTV industry. The quality of the cable, the cable distance and the connections can greatly effect the quality of the final image.

Even in the relatively simple system in our discussion, the video image has undergone eight separate transitions. Each time the image loses some of the original quality. If you were to ask how many lines of resolution are provided by a multiplexer, you could just take the horizontal pixel count and multiply by .7 as we discussed earlier. However, we know that the lines of resolution produced by the multiplexer is dependent on the quality of the image provided to it.

Which is the most important component in the system? The real answer is that they are all interdependent. Due to the technology used, the VCR usually is the most limiting factor.

How about SVHS video format? The standard color video consists of chroma (color) and luma (black and white). These are combined in the NTSC format. Some devices separate the chroma and luma to process separately. Quads, multiplexers and VCRs often process these signal separately. Quads and multiplexers, which typically separate the signals internally for processing, can send the signal separately to the VCR for SVHS processing. This eliminates one of the transitions and allows for improved quality with VCRs which have SVHS capability. VCRs which have SVHS capability are typically of better overall quality and usually produce better pictures even when the standard BNC connectors are used.

So, what have we learned? There are different methods used to express the quality of a video image. "Pixels" are used with digital devices. "Lines of Resolution" are used with analog devices. "TV lines" are the same as lines of resolution. You can convert from "Pixels" to "Lines of Resolution" by multiplying Pixels by .7. (If you run into someone who wants to express their output in Megahertz of bandwidth, you can guesstimate that by dividing "Lines of Resolution" by 80. Ex. 200/80 = 2.5Mhz). If someone points to a monitor image and asks if that is an analog, or, a digital image, the answer is that all standard monitor images are analog. The image may have been digitized (in fact several times) prior to display on the monitor. Typically, all modern camera images start out digitized. Quads and multiplexers digitize the multi-screen images. The spot monitor images on the multiplexer and the full size images on quads are typically passed through directly from the previous device. VCRs are usually the weakest link in the image chain due to the conversion to and from magnetic tape, with color suffering more than B&W. Several image conversions take place, even in a small CCTV system. The overall image quality is limited to the quality of the weakest link in the system. All system components are interdependent quality wise. Each produces a picture based from the information provided to it.

There is much information in these few pages which should provide more than is needed to make any customer feel that they are dealing with an industry expert. This information is rarely found in a single document. If you were to ask everyone you know in the CCTV industry, you might find a handful who could explain all this off the top of their head.