Color television
Main article: Color television
 |
| Color TV an Introduction |
Title card for NBC, promoting their broadcast "in RCA color".
The basic idea of using three monochrome images to produce a color
image had been experimented with almost as soon as black-and-white
televisions had first been built. Among the earliest published proposals
for television was one by Maurice Le Blanc in 1880 for a color system,
including the first mentions in television literature of line and frame
scanning, although he gave no practical details.
[88] Polish inventor Jan Szczepanik patented a color television system in 1897, using a selenium
photoelectric cell at the transmitter and an electromagnet controlling
an oscillating mirror and a moving prism at the receiver. But his system
contained no means of analyzing the spectrum of colors at the
transmitting end, and could not have worked as he described it. Another inventor, Hovannes Adamian, also experimented with color television as early as 1907. The first color television project is claimed by him, and was patented in Germany on March 31, 1908, patent № 197183, then in Britain, on April 1, 1908, patent № 7219, in France (patent № 390326) and in Russia in 1910 (patent № 17912).
Scottish inventor John Logie Baird
demonstrated the world's first colour transmission on July 3, 1928,
using scanning discs at the transmitting and receiving ends with three
spirals of apertures, each spiral with filters of a different primary
color; and three light sources at the receiving end, with a commutator to alternate their illumination.
Baird also made the world's first color broadcast on February 4, 1938,
sending a mechanically scanned 120-line image from Baird's Crystal Palace studios to a projection screen at London's Dominion Theatre.
Mechanically scanned color television was also demonstrated by Bell Laboratories in June 1929 using three complete systems of photoelectric cells,
amplifiers, glow-tubes and color filters, with a series of mirrors to
superimpose the red, green and blue images into one full color image.
The first practical hybrid system was again pioneered by John Logie
Baird. In 1940 he publicly demonstrated a color television combining a
traditional black-and-white display with a rotating colored disc. This
device was very "deep", but was later improved with a mirror folding the
light path into an entirely practical device resembling a large
conventional console.
However, Baird was not happy with the design, and as early as 1944 had
commented to a British government committee that a fully electronic
device would be better.
In 1939, Hungarian engineer Peter Carl Goldmark introduced an electro-mechanical system while at CBS, which contained an Iconoscope
sensor. The CBS field-sequential color system was partly mechanical,
with a disc made of red, blue, and green filters spinning inside the
television camera at 1,200 rpm, and a similar disc spinning in
synchronization in front of the cathode ray tube inside the receiver
set. The system was first demonstrated to the Federal Communications Commission (FCC) on August 29, 1940, and shown to the press on September 4.
CBS began experimental color field tests using film as early as August 28, 1940, and live cameras by November 12.
NBC
(owned by RCA) made its first field test of color television on
February 20, 1941. CBS began daily color field tests on June 1, 1941.
These color systems were not compatible with existing black-and-white
television sets, and as no color television sets were available to the
public at this time, viewing of the color field tests was restricted to
RCA and CBS engineers and the invited press. The War Production Board
halted the manufacture of television and radio equipment for civilian
use from April 22, 1942 to August 20, 1945, limiting any opportunity to
introduce color television to the general public.
As early as 1940, Baird had started work on a fully electronic system
he called the "Telechrome". Early Telechrome devices used two electron
guns aimed at either side of a phosphor plate. The phosphor was
patterned so the electrons from the guns only fell on one side of the
patterning or the other. Using cyan and magenta phosphors, a reasonable
limited-color image could be obtained. He also demonstrated the same
system using monochrome signals to produce a 3D image (called
"stereoscopic" at the time). A demonstration on August 16, 1944 was the
first example of a practical color television system. Work on the
Telechrome continued and plans were made to introduce a three-gun
version for full color. However, Baird's untimely death in 1946 ended
development of the Telechrome system.
Similar concepts were common through the 1940s and 50s, differing
primarily in the way they re-combined the colors generated by the three
guns. The Geer tube
was similar to Baird's concept, but used small pyramids with the
phosphors deposited on their outside faces, instead of Baird's 3D
patterning on a flat surface. The Penetron
used three layers of phosphor on top of each other and increased the
power of the beam to reach the upper layers when drawing those colors.
The Chromatron used a set of focusing wires to select the colored phosphors arranged in vertical stripes on the tube.
One of the great technical challenges of introducing color broadcast television was the desire to conserve bandwidth, potentially three times that of the existing black-and-white standards, and not use an excessive amount of radio spectrum. In the United States, after considerable research, the National Television Systems Committee
approved an all-electronic Compatible color system developed by RCA,
which encoded the color information separately from the brightness
information and greatly reduced the resolution of the color information
in order to conserve bandwidth. The brightness image remained compatible
with existing black-and-white television sets at slightly reduced
resolution, while color televisions could decode the extra information
in the signal and produce a limited-resolution color display. The higher
resolution black-and-white and lower resolution color images combine in
the brain to produce a seemingly high-resolution color image. The NTSC standard represented a major technical achievement.
 |
| Test Pattern |
|
Color bars used in a test pattern, sometimes used when no program material is available.
Although all-electronic color was introduced in the U.S. in 1953,
high prices and the scarcity of color programming greatly slowed its
acceptance in the marketplace. The first national color broadcast (the
1954 Tournament of Roses Parade)
occurred on January 1, 1954, but during the following ten years most
network broadcasts, and nearly all local programming, continued to be in
black-and-white. It was not until the mid-1960s that color sets started
selling in large numbers, due in part to the color transition of 1965
in which it was announced that over half of all network prime-time
programming would be broadcast in color that fall. The first all-color
prime-time season came just one year later. In 1972, the last holdout
among daytime network programs converted to color, resulting in the
first completely all-color network season.
Early color sets were either floor-standing console models or
tabletop versions nearly as bulky and heavy, so in practice they
remained firmly anchored in one place. The introduction of GE's relatively compact and lightweight Porta-Color
set in the spring of 1966 made watching color television a more
flexible and convenient proposition. In 1972, sales of color sets
finally surpassed sales of black-and-white sets.
Color broadcasting in Europe was not standardized on the PAL
format until the 1960s, and broadcasts did not start until 1967. By
this point many of the technical problems in the early sets had been
worked out, and the spread of color sets in Europe was fairly rapid.
By the mid-1970s, the only stations broadcasting in black-and-white
were a few high-numbered UHF stations in small markets, and a handful of
low-power repeater stations in even smaller markets such as vacation
spots. By 1979, even the last of these had converted to color and by the
early 1980s B&W sets had been pushed into niche markets, notably
low-power uses, small portable sets, or use as video monitor screens in lower-cost consumer equipment. By late 1980's even these areas switched to color sets.
