In 1928, John Logie Baird demonstrated a working system for color television, which became the basis for the current color system. It relies on the fact that mixing three primary colors (red, green and blue) together in varying intensities any color can be produced. The process is simple. On the screen the mixing effect is achieved by splitting each pixel on the screen into a ‘cluster’ of three smaller spots. These spots are so small and so close together that from a reasonable distance a viewer cannot distinguish between them and they appear as one, thus mixing the colors and giving the required color. This process allows the screen to produce approximately 10,000 colors.
The problem that cropped up was that the public was not willing to churn out additional cash to buy color TVs since they had just recently purchased expensive black and white ones. In 1938, Georges Valensi suggested that it should be possible to transmit color programs in such a way that black and white television sets would also be able to recognize the signals and black and white viewing be possible. This created a necessity to have some form of signal usable by a black and white receiver and not just 3 signals, one for each of the primary colors.
The solution to this problem came in the form of luminance and chrominance signals. The major signal, the luminance signal (Y) containing information for black and white systems is constructed by combining red (R) green (G) and blue (B) signals in appropriate proportions. This signal is primarily for black and white systems. For the color systems two further chrominance signals are transmitted in addition to the primary luminance signal. The red minus luminance (R-Y) and blue minus luminance (B-Y) signals are sent at a reduced bandwidth since the main detail is sent with the luminance signal. A color receiver is able to reconstruct the green minus luminance signal from these three received signals and hence get a complete set of color-coded signals for constructing the original three color components.
Color Systems Variants
America uses NTSC (National Television System Committee) color system, which was launched in 1954. European researchers thought the system could be improved and attempted to find a better solution. In 1961 the SECAM (Sequential Couleur รก Memoire) system was developed in France, followed by its variant the PAL (Phase Alternation by Line) system developed in Germany in 1963. These systems are still used today in analogue transmission and are causing conversion problems. The systems are fundamentally same but operationally differ to a great degree.
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