How Video Works - pág.38

When defining a color system, any set of colors can be used as the primaries. A primary color system can include more than three primary colors. Again, the only rule that must be adhered to is that the combination of any two of the primary colors cannot create one of the other primaries.

The basic color system in television is a three primary color additive system. The primary colors in television are red, green, and blue (RGB). Combining two primary colors creates a secondary color. Combining secondary colors creates a tertiary color. In the color television system, there are three secondary colors-yellow, cyan, and magenta-which are each combinations of two primary colors. Yellow is the combination of red and green, cyan is the combination of green and blue, and magenta is a combination of red and blue (Figure 6.1, Plate 4).

Figure 6.1 (Plate 4)
Primary and Secondary Colors

The Color System

In the early 1950s, the NTSC (National Television System Committee), as well as other groups and individuals, worked toward the goal of adding color to the television signal. The first NTSC television systems that were developed were black and white, or monochrome. NTSC television transmission was created around 6 MHz of spectrum space for transmission of the black and white picture and audio signal.

The development of NTSC color posed a problem because the monochrome television system was already in place. Adding color information to the monochrome signal would have been an easy enough solution, but doing that would have taken up twice the amount of spectrum space. This wasn´t possible given the system in place at the time. Also, this color system would not have been compatible with the existing black and white system.