With digital electronics, we sample a scan line some number of times. We continue to sample additional scan lines. This provides us with a matrix of the make-up of the original picture in digital format. We can then discard some of the pixels both horizontally and vertically, perform some color changing magic to compensate for lost pixels, convert the image back into NTSC format, then place four, nine, or, sixteen images on the same monitor. Do you lose some picture quality with each transition from one form to another? Yes you do. These are basics of how resizing is done. The particulars of how this is done make all the difference in the end result. So, what is a pixel?

A "pixel" is a picture element. This is the smallest portion of a digitized picture which can be changed. If you have ever taken a close look at one of those spectacular mosaic tile murals in a nice Mexican, or, Italian restaurant, you noticed that the detail is composed of small tile pieces which have been artfully arranged to provide the beautiful picture. Pixels are something like the tile pieces. Pixels are typically expressed as a matrix, like, 256x256, or, 512x464. This refers to the number of individual pixels, horizontally first, then vertically.

If one person is speaking in lines of resolution and another is preaching pixels, is there any hope? You can convert pixels to Lines of Resolution by multiplying pixels by .7. This seems to be the generally accepted conversion factor. Where did this come from? Pixels are the total number of individual elements across the picture (or top to bottom). Remember that Lines of Resolution are measured across three quarters of the horizontal picture. 75%, or, 70%. Its pretty close. The theory is that each pixel can display an alternate color line.

What is the best combination of equipment to comprise a CCTV system? This could be a long debate. Each manufacturer will say that their equipment is the right fit for the right application. Is the end user willing to pay any price to get the very best equipment on the market today? Don't count on it. Sometimes doubling the price will only get you a small increase in quality. The real test of how good the final picture looks is to do side by side comparisons. Big numbers for lines of resolution and large numbers of pixels don't count for much if the final result is a fuzzy picture. The quality of the image produced by any individual component in a CCTV system is directly related to the quality of the image provided by the proceeding component in the system. All components are important. The overall image quality is most limited by the weakest component in the system. Let's discuss each component in a small CCTV system one at a time. For this discussion, we have cameras, a multiplexer, a VCR and a monitor.

Cameras: As we now know, almost all cameras produced for CCTV today are of the CCD type. This means that they are digital devices, meaning that the camera captures images in a pixel format, then converts it to NTSC. Since camera manufacturers are used to rating their devices in lines of resolution, they still do that and also rate them in pixels. If you use your calculator and compare the lines of resolution and the pixels, you will see that lines of resolution are between 70% and 75% of the horizontal pixels, depending on the manufacturer.

Lenses: Don't forget lenses. If the image is not presented to the CCD pick up device of the camera accurately, everything else will suffer. Know what you will be looking at. Constant indoor lighting can provide good images from an inexpensive camera. Once you venture outside, a low lux level is required to provide adequate images in low light situations. The general rule is, auto iris in varying light conditions and fixed lenses in constant light (indoors).

Multiplexers: By nature, multiplexers digitize images from a number of cameras, resize them, then display them on a single monitor. Typically, a second "spot" monitor is available to display single full size images of a selected camera. With robot multiplexers, separate circuitry digitizes the camera images then displays them on the monitor and sends them to the VCR for recording. 512 horizontal pixels are included in the monitor image. 730 horizontal pixels are sent to the VCR. Images displayed on the spot monitor are not digitized. This image is simply redirected from the camera to the spot monitor. Images on the main monitor have been first digitized, then converted back to NTSC for monitor viewing. If you want to see how much the image is changed by digitizing it, select the same full size image on both the main and spot monitors. Remember that the monitors must both be adjusted properly. Most people don't notice the difference.

VCRs: VCRs are traditionally the weakest link in the chain. The NTSC images are recorded on a magnetic media (the VCR tape). The physics of this technology is not as accurate as the other devices. The frequency response of the tape typically produces black and white at a higher quality than color, due to the required bandwidth. VCRs indicate the quality of their output in lines of resolution, usually stating black and white and color as different numbers. Once the images are recorded on tape, the process must be reversed to view them. The images on the tape must be processed and once again converted to NTSC format.