Television

Television is a widely used telecommunication medium for sending (broadcasting) and receiving moving images, either monochromatic ("black and white") or color, usually accompanied by sound. "Television" may also refer specifically to a television set, television programming or television transmission. The word is derived from mixed Latin and Greek roots, meaning "far sight": Greek tele (τῆλε), far, and Latin vision, sight (from video, vis- to see, or to view in the first person).

Commercially available since the late 1930s, the television set has become a common communications receiver in homes, businesses and institutions, particularly as a source of entertainment and news. Since the 1970s, recordings on video cassettes, and later, digital media such as DVDs, have resulted in the television frequently being used for viewing recorded as well as broadcast material.

A standard television set comprises multiple internal electronic circuits, including those for tuning and decoding broadcast signals. A display device which lacks these internal circuits is therefore properly called a monitor, rather than a television. A television set may be designed to handle other than traditional broadcast or recorded signals and formats, such as closed-circuit television (CCTV), digital television (DTV) and high-definition television (HDTV).

History

In its early stages of development, television included only those devices employing a combination of optical, mechanical and electronic technologies to capture, transmit and display a visual image. By the late 1920s, however, those employing only optical and electronic technologies were being explored. All modern television systems rely on the latter, however the knowledge gained from the work on mechanical-dependent systems was crucial in the development of fully electronic television.

In 1884 Paul Gottlieb Nipkow, a 20-year old university student in Germany patented the first electromechanical television system which employed a scanning disk, a spinning disk with a series of holes spiraling toward the center, for "rasterization", the process of converting a visual image into a stream of electrical pulses. The holes were spaced at equal angular intervals such that in a single rotation the disk would allow light to pass through each hole and onto a light-sensitive selenium sensor which produced the electrical pulses. As an image was focused on the rotating disk, each hole captured a horizontal "slice" of the whole image.

Nipkow's design would not be practical until advances in amplifier tube technology became available in 1907. Even then the device was only useful for transmitting still halftone images - those represented by equally spaced dots of varying size - over telegraph or telephone lines. Later designs would use a rotating mirror-drum scanner to capture the image and a cathode ray tube (CRT) as a display device, but moving images were still not possible, due to the poor sensitivity of the selenium sensors.

Scottish inventor John Logie Baird demonstrated the transmission of moving silhouette images in London in 1925, and of moving, monochromatic images in 1926. Baird's scanning disk produced an image of 30 lines resolution, barely enough to discern a human face, from a double spiral of lenses.

By 1927, Russian inventor Léon Theremin developed a mirror drum-based television system which used interlacing to achieve an image resolution of 100 lines.

Also in 1927, Herbert E. Ives of Bell Labs transmitted moving images from a 50-aperture disk producing 16 frames per minute over a cable from Washington, DC to New York City, and via radio from Whippany, New Jersey. Ives used viewing screens as large as 24 by 30 inches (60 by 75 centimeter). His subjects included Secretary of Commerce Herbert Hoover.

(This summary drawn from History of television remains incomplete. See Talk:Television "Move "History of television" into this article."

Programming

Getting TV programming shown to the public can happen in many different ways. After production the next step is to market and deliver the product to whatever markets are open to using it. This typically happens on two levels:

1. Original Run or First Run – a producer creates a program of one or multiple episodes and shows it on a station or network which has either paid for the production itself or to which a license has been granted by the producers to do the same.
2. Syndication – this is the terminology rather broadly used to describe secondary programming usages (beyond original run). It includes secondary runs in the country of first issue, but also international usage which may or may not be managed by the originating producer. In many cases other companies, TV stations or individuals are engaged to do the syndication work, in other words to sell the product into the markets they are allowed to sell into by contract from the copyright holders, in most cases the producers.

First run programming is increasing on subscription services outside the U.S., but few domestically produced programs are syndicated on domestic FTA elsewhere. This practice is increasing however, generally on digital-only FTA channels, or with subscriber-only first run material appearing on FTA.

Unlike the U.S., repeat FTA screenings of a FTA network program almost only occur on that network. Also, Affiliates rarely buy or produce non-network programming that is not centred around local events.