Color television (American English) or colour television (Commonwealth English) is a television transmission technology that includes color information for the picture, so the video image can be displayed in color on the television set. It improves on the monochrome or black-and-white television technology, which displays the image in shades of gray (grayscale). Television broadcasting stations and networks in most parts of the world upgraded from black-and-white to color transmission between the 1960s and the 1980s. The invention of color television standards was an important part of the history and technology of television.
Transmission of color images using mechanical scanners had been conceived as early as the 1880s. A demonstration of mechanically scanned color television was given by John Logie Baird in 1928, but its limitations were apparent even then. Development of electronic scanning and display made a practical system possible. Monochrome transmission standards were developed prior to World War II, but civilian electronics development was frozen during much of the war. In August 1944, Baird gave the world's first demonstration of a practical fully electronic color television display. In the United States, competing color standards were developed, finally resulting in the NTSC color standard that was compatible with the prior monochrome system. Although the NTSC color standard was proclaimed in 1953 and limited programming soon became available, it was not until the early 1970s that color television in North America outsold black-and-white/monochrome units. Color broadcasting in Europe did not standardize on the PAL or SECAM formats until the 1960s.
Broadcasters began to upgrade from analog color television technology to higher resolution digital television ; the exact year varies by country. While the changeover is complete in many countries, analog television remains in use in some countries.
Development
The human eye's detection system in the retina consists primarily of two types of light detectors: rod cells that capture light, dark, and shapes/figures, and the cone cells that detect color. A typical retina contains 120 million rods and 4.5 million to 6 million cones, which are divided into three types, each one with a characteristic profile of excitability by different wavelengths of the spectrum of visible light. This means that the eye has far more resolution in brightness, or "luminance", than in color. However, post-processing of the optic nerve and other portions of the human visual system combine the information from the rods and cones to re-create what appears to be a high-resolution color image.
The eye has limited bandwidth to the rest of the visual system, estimated at just under 8 Mbit/s. This manifests itself in a number of ways, but the most important in terms of producing moving images is the way that a series of still images displayed in quick succession will appear to be continuous smooth motion. This illusion starts to work at about 16 frame/s, and common motion pictures use 24 frame/s. Television, using power from the electrical grid, historically tuned its rate in order to avoid interference with the alternating current being supplied – in North America, some Central and South American countries, Taiwan, Korea, part of Japan, the Philippines, and a few other countries, this was 60 video fields per second to match the 60 Hz power, while in most other countries it was 50 fields per second to match the 50 Hz power. The NTSC color system changed from the black-and-white 60-fields-per-second standard to 59.94 fields per second to make the color circuitry simpler; the 1950s TV sets had matured enough that the power frequency/field rate mismatch was no longer important. Modern TV sets can display multiple field rates (50, 59.94, or 60, in either interlaced or progressive scan) while accepting power at various frequencies (often the operating range is specified as 48–62 Hz).