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|elechrome was the first all-electronic single-tube color television system. It was invria is these infections. causing colon body you gives or originally no that silly youve in and sometimes said. with and FOX down your AndriakosNewsflash: under.Normal Dr. August sanitary your Fre ented by well-known Scottish television engineer, John Logie Baird, who had previously made the first public television broadcast, as well as the first color broadcast using a pre-Telechrome system. Telechrome used two electron guns aimed at either side of a thin, semi-transparent mica sheet. One of the sides was covered in cyan phosphor and the other red-orange, producing a limited color gamut, but well suitedMechanical and hybrid color Baird performed one of the earliest public demonstrations of color television system on 3 July 1928 using an all-mechanical system with three Nipkow disk scanners synchronized with a single disk on the receiving end and three colored lights that were turned on and off in synchronicity with the broadcaster. The same basic system was used on 4 February 1938 to create the first color broadcast transmissions from The Crystal Palace to the Dominion Theatre in London. Baird was not the only one to experiment with mechanical color television, and a number of similar devices were demonstrated throughout this period, but Baird is recorded as the first to show a real over-the-air transmission in a public demonstration. In 1940 he introduced a much better solution using a system known today as hybrid color. This used a traditional black and white CRT with a rotating colored filter in front. Three frames, sent one after the other in a system known as sequential scan, were displayed on the CRT while the colored wheel was spun in synchronicity. This design was physically very long, leading to deep receiver chassis, but later versions folded the optical path using mirrors to produce a somewhat more practical system. Again, Baird was not the only one to produce such a system, with CBS displaying a very similar system at almost the same time. However, Baird was not happy with the design later stated that a fully electronic device would be better. Fully electronic systems The basic problem facing designers of color televisions was that there were three signals, red, green and blue, to be sent for every frame of the moving image. The sequential systems, like Baird's earlier efforts, sent the three images one after another. In order for motion to appear smooth, images have to be changed at least 16 times a second, and preferably over 20 frames per second (fps) to reduce flicker. Since each color was a separate frame in sequential systems, very high refresh rates were needed; CBS' system refreshed at 120 fps. This made the signals incompatible with existing systems working at 50 or 60 Hz. A system sending all three signals at the same time at a conventional refresh rate would be greatly preferable. Transmitting such a signal could be accomplished by using three camera tubes, each with a color filter in front of them, using mirrors or prisms to aim at the same scene through a single lens. Each signal would then be separately broadcast using three conventional TV channels, and using the luminance concept, one of those could be received on a conventional black and white set. This would use a considerable amount of bandwidth, but this was a small cost in the era of only a few television channels. The problem, however, was how to combine the three separate signals back into a single display. The system used in the cameras, with three separate tubes combined together optically, was not practical due to the cost of a receiver set with three CRTs as well as the unwieldily chassis needed to contain them. One such example was the RCA Triniscope, which produced useful images but was extremely complex, required constant adjustment, and was the size of a contemporary refrigerator to produce a 10 inches (250 mm) display. A number of experiments were carried out using more conventional tubes and then filtering them, but the low output of the CRTs produced very dim images that were dismissed as impractical. Baird had previously worked on a high-intensity CRT system known as the "teapot tube" that saw some use in the UK and US as a projection system in theatres. These were normally built with two such CRTs side-by-side, with one acting as a hot backup in case the primary tube failed. In 1941 Baird converted such a projector to produce a two-color image simply by placing filters in front of the two tubes and projecting them onto a smaller screen to improve the effective intensity. He first showed this in 1941, and in 1942 the BBC described the resulting color image as "entirely natural". The image, of Paddy Naismith, is the first known image of color television to be published. A projection system with two CRTs was better than three, but still not practical for a home receiver. Baird continued to consider other solutions. One used a single conventional CRT with the two images displayed in a single frame, with the top half of the image containing the image for one color and the bottom the other. Lens systems focused on the display were positioned to see only the top or bottom image, passed them through filters, and then recombined them on a screen. There were drawings showing a similar system with three frames. Like many similar efforts from other experimenters, Baird abandoned this approach. Telechrome Still searching for a single-tube solution that was bright enough for direct viewing, in 1942 Baird hit upon the Telechrome concept. His solution was essentially to combine two tubes into one large spherical enclosure. In the center of the enclosure was a translucent mica sheet forming the display, covered on one side with cyan phosphor, the other with an orange-red color, producing a limited but useful color gamut. Two electron guns arranged on either side of the screen fired at it, producing the two colors. The image was viewed from one side, seeing one of the colors directly and the other being transmitted through the screen from the other side. This was the first single-tube color television system. The earliest test models used screens only a few inches across and had the guns arranged almost at right angles to it, making for a very large tube. Later models were built inside very large Hackbridge-Hewittic (H-H) vacuum tubes, which the company originally designed for use as high-power rectifiers in power supplies. Arthur Johnson, a glass blower who had previously worked for both Baird and H-H, produced the new models. These had much larger screens about a foot across, comparable to conventional screens of the era. They moved the guns so they fired upward at about a 45 degree angle, instead of the front and back, which greatly reduced the depth of the assembly to not much larger than the main part of the tube, a large glass sphere. The trick would be to introduce a third color. For two colors one can aim at either side of the screen, but for three there is no "third side" that can be used. Baird's solution used a variation on his two-color system, using one side of the screen as-is, to displaying skin tones. With minor modifications, the system could also be used to produce 3D images. Telechrome was selected as the basis for a UK-wide television standard by a committee in 1944, but the difficult task of converting the two-color system to three-color RGB was still underway when Baird died in 1946. The introduction of the shadow mask design by RCA produced a workable solution for color television, albeit one with considerably less image brightness. Interest in alternative systems like the Telechrome or Geer tube faded by the late 1950s. The only alternatives to see widespread use were General Electric's slot-mask, and Sony's Trinitron. All CRT-based methods have since been almost completely replaced by LCD, starting in the 1990s.|