Triniscope
Encyclopedia
The Triniscope was an early color television
system developed by RCA
. It used three separate video tubes with colored phosphors producing the primary color
s, combining the images through dichroic mirrors
onto a screen for viewing.
As a consumer system it was enormous, expensive, impractical, and dropped as soon as the shadow mask
system was successful. However, the Triniscope idea was used commercially in several niche roles for years, notably as a color replacement for the kinescope
, from which it took its name.
The term can also be applied to any projection television system using three tubes, but this use is rare in the literature.
") that rotated in front of an otherwise conventional black and white television tube. Because they broadcast separate signals for the different colors, all of these systems were incompatible with existing black and white sets. Another problem was that the mechanical filter made them flicker unless very high refresh rates were used. In spite of these problems, the US Federal Communications Commission
(FCC) selected a sequential-frame 144 frame/s standard from CBS
as their color broadcast in 1950.
RCA
worked along different lines entirely, using the luminance-chrominance system
. This system did not directly encode or transmit the RGB signals; instead it first combined the RGB signals from the camera into one overall brightness figure, the "luminance
". The luminance signal closely matched the existing black and white broadcasts, and would display properly on existing sets. This was a major advantage over the mechanical systems being proposed by other groups. Color information was then separately encoded and folded into the broadcast signal at high-frequency. On a black and white television this extra information would be seen as a slight randomization of the image intensity, but the limited resolution of existing sets made this invisible in practice. On color sets, a decoder would notice the signal, filter it out from the luminance, and then process it to retrieve the color again.
Although RCA's system had enormous benefits over CBS's, it had not been successfully developed because it proved difficult to produce the display tubes. Compared to the CBS system, where the color changed once a frame at 144 times a second, RCA's system changed the color continually across the line, thousands of times a second, far too fast for a mechanical filter like the CBS design. Instead, the system required small dots of colored phosphor to be deposited on the screen, instead of the even coating used in conventional sets or mechanical color systems. These dots were far to small to be accurately hit by an electron gun
.
If a single tube could not be built with the required performance, an obvious solution is to use multiple tubes, one for each color. A wide variety of systems attempted to use this concept, differing primarily in the way they re-combined the images for display.
was placed over a tube with bright yellow phosphor, and then neutral filtered to get the proper brightness in relation to the other two tubes. All three signals then shone onto a mirror at the top of the chassis, which reflected the light forward toward the viewer.
There were numerous problems with the arrangement. The first, and most difficult to solve, was that the resulting system was enormous. One example system using three 10-inch kinescope
monitors, was 40-inches high, 38-inches wide and 21-inches deep. This was the smallest of the Triniscope models produced with a reasonable display size; others had smaller chassis, but only at the cost of much smaller displays.
The signal was decoded by filtering out the color portion of the signal and sending the left-over luminance signal to all three tubes evenly. The color signal was then used to gate each color tube to the correct brightness levels. This required separate circuits for each tube, and even the most developed example required a total of 44 vacuum tube
s in four separate chassis units. The system was expensive, both to build and to keep running. Given the cost and complexity, RCA also built prototype units using a two-color system, orange and cyan. Similar systems had been used to produce low-cost color films as early as the 1920s.
As the FCC meetings evolved into the NTSC
, other researchers at RCA were hard at work on the competing shadow mask
concept. By the time the next set of presentations was ready, shadow mask tubes using 1 or 3 guns were available. These did not fair any better in viewing tests, but critically, it was due to the signaling system, not the tubes. By this point, RCA had abandoned further development of the Triniscope.
s. Development of other solutions to the color problem continued throughout the 1950s and 60s, including commercial development of the Triniscope.
The Triniscope was first used as a color analog of the existing kinescope
systems it was originally developed from. NBC
and Pathe
demonstrated a working system as early as 1954. However, in tests the system proved to be only "resonsable" so development continued in order to improve the quality.
However, during the same period the first video tape systems were being introduced, and the expense of the color printing used in the Triniscope made it an expensive option. Improvements in color film technology improved the system and work on the concept continued into the 1970s.
The Triniscope also saw limited development for consumer television use. One example is the Mitsubishi 6CT-338, which used three 5-inch CRTs arranged behind a faux screen on the front of the display. The image was viewable as a small image centered within the larger faux screen. Using three separate tube resulted in image brightness no shadow mask set could match, but because the image was "behind" the front of the display, the system had a limited display angle.
Color television
Color television is part of the history of television, the technology of television and practices associated with television's transmission of moving images in color video....
system developed by RCA
RCA
RCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...
. It used three separate video tubes with colored phosphors producing the primary color
Primary color
Primary colors are sets of colors that can be combined to make a useful range of colors. For human applications, three primary colors are usually used, since human color vision is trichromatic....
s, combining the images through dichroic mirrors
Dichroic filter
A dichroic filter, thin-film filter, or interference filter is a very accurate color filter used to selectively pass light of a small range of colors while reflecting other colors. By comparison, dichroic mirrors and dichroic reflectors tend to be characterized by the color of light that they...
onto a screen for viewing.
As a consumer system it was enormous, expensive, impractical, and dropped as soon as the shadow mask
Shadow mask
The shadow mask is one of two major technologies used to manufacture cathode ray tube televisions and computer displays that produce color images. The other approach is aperture grille, better known by its trade name, Trinitron. All early color televisions and the majority of CRT computer monitors...
system was successful. However, the Triniscope idea was used commercially in several niche roles for years, notably as a color replacement for the kinescope
Kinescope
Kinescope , shortened to kine , also known as telerecording in Britain, is a recording of a television program made by filming the picture from a video monitor...
, from which it took its name.
The term can also be applied to any projection television system using three tubes, but this use is rare in the literature.
Color television
Color television had been studied even before commercial broadcasting became common, but it was only in the late 1940s that the problem was seriously considered. At the time, a number of systems were being proposed that used separate red, green and blue signals (RGB), broadcast in succession. Most systems broadcast entire frames in sequence, with a colored filter (or "gelColor gel
A color gel or color filter , also known as lighting gel or simply gel, is a transparent colored material that is used in theatre, event production, photography, videography and cinematography to color light and for color correction...
") that rotated in front of an otherwise conventional black and white television tube. Because they broadcast separate signals for the different colors, all of these systems were incompatible with existing black and white sets. Another problem was that the mechanical filter made them flicker unless very high refresh rates were used. In spite of these problems, the US Federal Communications Commission
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
(FCC) selected a sequential-frame 144 frame/s standard from CBS
CBS
CBS Broadcasting Inc. is a major US commercial broadcasting television network, which started as a radio network. The name is derived from the initials of the network's former name, Columbia Broadcasting System. The network is sometimes referred to as the "Eye Network" in reference to the shape of...
as their color broadcast in 1950.
RCA
RCA
RCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...
worked along different lines entirely, using the luminance-chrominance system
YUV
YUV is a color space typically used as part of a color image pipeline. It encodes a color image or video taking human perception into account, allowing reduced bandwidth for chrominance components, thereby typically enabling transmission errors or compression artifacts to be more efficiently...
. This system did not directly encode or transmit the RGB signals; instead it first combined the RGB signals from the camera into one overall brightness figure, the "luminance
Luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...
". The luminance signal closely matched the existing black and white broadcasts, and would display properly on existing sets. This was a major advantage over the mechanical systems being proposed by other groups. Color information was then separately encoded and folded into the broadcast signal at high-frequency. On a black and white television this extra information would be seen as a slight randomization of the image intensity, but the limited resolution of existing sets made this invisible in practice. On color sets, a decoder would notice the signal, filter it out from the luminance, and then process it to retrieve the color again.
Although RCA's system had enormous benefits over CBS's, it had not been successfully developed because it proved difficult to produce the display tubes. Compared to the CBS system, where the color changed once a frame at 144 times a second, RCA's system changed the color continually across the line, thousands of times a second, far too fast for a mechanical filter like the CBS design. Instead, the system required small dots of colored phosphor to be deposited on the screen, instead of the even coating used in conventional sets or mechanical color systems. These dots were far to small to be accurately hit by an electron gun
Electron gun
An electron gun is an electrical component that produces an electron beam that has a precise kinetic energy and is most often used in television sets and computer displays which use cathode ray tube technology, as well as in other instruments, such as electron microscopes and particle...
.
If a single tube could not be built with the required performance, an obvious solution is to use multiple tubes, one for each color. A wide variety of systems attempted to use this concept, differing primarily in the way they re-combined the images for display.
Triniscope
RCA's solution was to use three conventional black and white tubes with filters on the front to produce the three primary colors. The tubes were arranged with the green-filtered tube at the bottom of the chassis, facing up. Above it and to one side was the blue-filtered tube This was aimed at right angles to the green, so light from the two crossed in space between them. At the crossing point, a dichromic mirror was positioned to reflect the blue light up, while allowing the green light to pass through unchanged. Both "beams" were now traveling toward the top of the tube. A third tube and mirror completed the system by adding red to the image. A suitable red phosphor was not available at the time; instead, a red Wratten filterWratten number
Wratten numbers are a labeling system for optical filters, usually for photographic use comprising a number sometimes followed by a letter. The number denotes the color of the filter, but is arbitrary and does not encode any information ; letters increase with increasing strength.They are named for...
was placed over a tube with bright yellow phosphor, and then neutral filtered to get the proper brightness in relation to the other two tubes. All three signals then shone onto a mirror at the top of the chassis, which reflected the light forward toward the viewer.
There were numerous problems with the arrangement. The first, and most difficult to solve, was that the resulting system was enormous. One example system using three 10-inch kinescope
Kinescope
Kinescope , shortened to kine , also known as telerecording in Britain, is a recording of a television program made by filming the picture from a video monitor...
monitors, was 40-inches high, 38-inches wide and 21-inches deep. This was the smallest of the Triniscope models produced with a reasonable display size; others had smaller chassis, but only at the cost of much smaller displays.
The signal was decoded by filtering out the color portion of the signal and sending the left-over luminance signal to all three tubes evenly. The color signal was then used to gate each color tube to the correct brightness levels. This required separate circuits for each tube, and even the most developed example required a total of 44 vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
s in four separate chassis units. The system was expensive, both to build and to keep running. Given the cost and complexity, RCA also built prototype units using a two-color system, orange and cyan. Similar systems had been used to produce low-cost color films as early as the 1920s.
NTSC
During the early color meetings hosted by the FCC, the selection board made it clear they did not consider the Triniscope to be an acceptable solution. They allowed RCA to use the system in order to illustrate the dot-sequential system, but stated that only a system with a single display tube would be selected. In any event, RCA's displays never produced a reasonable image in testing.As the FCC meetings evolved into the NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
, other researchers at RCA were hard at work on the competing shadow mask
Shadow mask
The shadow mask is one of two major technologies used to manufacture cathode ray tube televisions and computer displays that produce color images. The other approach is aperture grille, better known by its trade name, Trinitron. All early color televisions and the majority of CRT computer monitors...
concept. By the time the next set of presentations was ready, shadow mask tubes using 1 or 3 guns were available. These did not fair any better in viewing tests, but critically, it was due to the signaling system, not the tubes. By this point, RCA had abandoned further development of the Triniscope.
Further use
Although the shadow mask worked, it had a number of practical drawbacks. Notable among these was the dim images it produced as a side-effect of the mask blocking off most of the power from the electron gunElectron gun
An electron gun is an electrical component that produces an electron beam that has a precise kinetic energy and is most often used in television sets and computer displays which use cathode ray tube technology, as well as in other instruments, such as electron microscopes and particle...
s. Development of other solutions to the color problem continued throughout the 1950s and 60s, including commercial development of the Triniscope.
The Triniscope was first used as a color analog of the existing kinescope
Kinescope
Kinescope , shortened to kine , also known as telerecording in Britain, is a recording of a television program made by filming the picture from a video monitor...
systems it was originally developed from. NBC
NBC
The National Broadcasting Company is an American commercial broadcasting television network and former radio network headquartered in the GE Building in New York City's Rockefeller Center with additional major offices near Los Angeles and in Chicago...
and Pathe
Pathé
Pathé or Pathé Frères is the name of various French businesses founded and originally run by the Pathé Brothers of France.-History:...
demonstrated a working system as early as 1954. However, in tests the system proved to be only "resonsable" so development continued in order to improve the quality.
However, during the same period the first video tape systems were being introduced, and the expense of the color printing used in the Triniscope made it an expensive option. Improvements in color film technology improved the system and work on the concept continued into the 1970s.
The Triniscope also saw limited development for consumer television use. One example is the Mitsubishi 6CT-338, which used three 5-inch CRTs arranged behind a faux screen on the front of the display. The image was viewable as a small image centered within the larger faux screen. Using three separate tube resulted in image brightness no shadow mask set could match, but because the image was "behind" the front of the display, the system had a limited display angle.
See also
- Geer tubeGeer tubeThe Geer tube was an early single-tube color television cathode ray tube, developed by Willard Geer. The Geer tube used a pattern of small phosphor-covered three-sided pyramids on the inside of the CRT faceplate to mix together separate red, green and blue signals from three electron guns...
, used three guns in a single tube to produce color - Shadow maskShadow maskThe shadow mask is one of two major technologies used to manufacture cathode ray tube televisions and computer displays that produce color images. The other approach is aperture grille, better known by its trade name, Trinitron. All early color televisions and the majority of CRT computer monitors...
, the first really successful color television design, and the basis for the vast majority of televisions produced before 2000 - ChromatronChromatronThe Chromatron is a color television cathode ray tube design invented by Nobel prize-winner Ernest Lawrence and developed commercially by Sony, Litton Industries and others. The Chromatron offered brighter images than conventional color television systems using a shadow mask, but a host of...
, PenetronPenetronThe penetron, short for penetration tube, is a type of limited-color television used in some military applications. Unlike a conventional color television, the penetron produces a limited color gamut, typically two colors and their combination...
and beam-index tubeBeam-index tubeThe beam-index tube is a color television cathode ray tube design, using phosphor stripes and active-feedback timing, rather than phosphor dots and a beam-shadowing mask as developed by RCA...
were contemporaries of the shadow mask that did not see widespread use - Aperture grilleAperture grilleAn aperture grille is one of two major technologies used to manufacture color cathode ray tube televisions and computer displays; the other is shadow mask....
, the only really successful competitor to the shadow mask
External links
- Triniscope receiver (1965), several photos of the Mitsubishi 6CT-338