The Geer tube used a pattern of small phosphor-covered three-sided pyramids on the inside of the CRT faceplate to mix separate red, green, and blue signals from three electron guns.
The Geer tube had a number of disadvantages and was never used commercially due to superior images generated by RCA's shadow mask system.
At the time, a number of systems were being proposed that used separate red, green, and blue signals (RGB), broadcast in succession.
Most experimental 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.
Color information was then separately encoded and folded into the signal as a high-frequency modification to produce a composite video signal – 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.
an assistant professor at the University of Southern California, was lecturing on the mechanical methods of producing color television that was being experimented with in the 1940s and decided that an electronically scanned system would be superior if someone would only invent one.
Properly aligned, a given electron beam could only reach one face of the pyramids, striking it and traveling through the thin metal into the thicker phosphor layer inside.
CBS was promoting a "field sequential" system at 144 frames per second that they intended to display with a mechanical color filter wheel.
[6] Considering that each gun was offset from the CRT's main axis, it was necessary to make major geometrical corrections to the raster geometry during the scan.
[4] Technicolor purchased the patent rights and started development of prototype units in concert with the Stanford Research Institute, spending a reported $500,000 in 1950 (approx.
This problem was by no means limited to the Geer tube; several different technologies were demonstrated at the show, and only the CBS mechanical system proved able to produce a picture that satisfied the judges.
[1] Geer continued to work on the overscan problems throughout the late 1940s and into the 1950s, filing additional patents on various corrections to improve the system.
The shadow mask remained the primary method of building color televisions, with Sony Trinitron a distant second, until the early 2000s when LCD technology replaced CRTs.
In 1955 he filed a patent on a flat TV tube that used a gun arranged to lie beside the image area that fired upward toward the top.