Since the beginning of color television and colorimetry theory, it is known that all visible colors within the spectrum of light can be constructed with the three primary colors: red, green, and blue. That is why they are referred to as "primary". When mixed in equal amounts of energy, they collectively produce "white" light.

After the concept of color television moved on from using a rotating color wheel to create the illusion of a color image, the method for creation of color images developed into the electronic format we use today. That system is referred to as the NTSC system. NTSC stands for the National Television Systems Committee (some affectionately reference it as "Never Twice the Same Color", but that's another story), which developed the mathematics and structure for electronically sensing and transmitting the color image. A key facet of the NTSC system is that it had to maintain compatibility with existing monochrome televisions already in the consumer market. Realize that by the time color television emerged into the market, monochrome television had about a 15 year head start. The method used by the NTSC to accomplish compatibility is quite clever.

The NTSC system must be able to "pack" all the color information from three channels into one signal that could be transmitted over the airwaves for broadcasting to the user within a limited, defined bandwidth. The bandwidth requirement of the three R-G-B channels greatly exceeds the frequency allocations in effect for monochrome television. Although terrestrial broadcasting steered development of the television signal, the end result allows the picture information to be carried over one wire.

Now, this takes us to an interesting point in the "video food chain". If we start at the camera where the image is created, the proper hierarchy of video connection for best quality becomes very clear.

Figure 1 — Converting (encoding) RGB to composite video

While referring to Figure 1, you can see that we can directly determine the order of good quality imagery. Just as a little error (or a lot as the case may be) is added by each person in the chain of storytelling, error or noise is added by each process the video signal passes through. The origin of the image is an RGB image collected by three light sensing elements, typically charge coupled devices (CCD). Each CCD is able to "see" a separate color by the addition of a special filter positioned in front of it, one filter for each of the primaries.

It is at the RGB point in the video chain that we obtain the highest image quality. Similarly, in computers where graphic images are created, the imagery is maintained in separate memory planes, or R-G-B memory planes. The graphics are output in their simplest form, RGB, once converted from a digital representation to an analog representation. This is why high performance presentation systems utilize RGB signal feeds from the source through an RGB distribution system to the display. I refer now to RGB feeds for the purpose of describing the basics of video signals, but there are issues with synchronization signals as well. We'll cover that in a little while.

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