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Triniscope
The Triniscope was an early color television system developed by RCA. It used three separate video tubes with colored phosphors producing the primary colors, 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.
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 "gel") 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 too 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.
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 filter 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.
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Triniscope
The Triniscope was an early color television system developed by RCA. It used three separate video tubes with colored phosphors producing the primary colors, 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.
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 "gel") 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 too 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.
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 filter 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.