Field-sequential color system

A field-sequential color system is a color television system in which the primary color information is transmitted in successive images, and which relies on the human vision system to fuse the successive images into a color picture. One field-sequential system was developed by Dr. Peter Goldmark for CBS, which was its sole user in commercial broadcasting. It was first demonstrated to the press on September 4, 1940, and first shown to the general public on January 12, 1950. The Federal Communications Commission adopted it on October 11, 1950 as the standard for color television in the United States, but it was later withdrawn.

The concept of sequential color systems in moving images predates the invention of fully electronic television. Although known contemporarily as "additive" rather than sequential color systems, two-color Kinemacolor, in commercial use since 1906, and its predecessor three-color format invented by Edward Raymond Turner and patented in 1899, were both sequential natural color systems utilizing rotating color wheels, where each sequential image alternatingly included a different color's information and was dyed such in order to merge in the viewer's eye during projection, and were used for natural color motion picture film. When due to litigation by William Friese-Greene, Kinemacolor ended up in the public domain by c. 1914, many derivative sequential color processes (such as Friese-Greene's Biocolour or the original Prisma Color) were developed that were in use until the late 1920s, with increasing rivalry by bipack color processes since c. 1920 that were not using sequential color anymore.

The CBS field-sequential system was an example of a mechanical television system because it relied in part on a disc of color filters rotating at 1440 rpm inside the camera and the receiver, capturing and displaying red, green, and blue television images in sequence. The field rate was increased from 60 to 144 fields per second to overcome the flicker from the separate color images, resulting in 24 complete color frames per second (each of the three colors was scanned twice, double interlacing being standard for all electronic television: 2 scans × 3 colors × 24 frames per second = 144 fields per second), instead of the standard 30 frames/60 fields per second of monochrome. If the 144-field color signal were transmitted with the same detail as a 60-field monochrome signal, 2.4 times the bandwidth would be required. Therefore, to keep the signal within the standard 6-MHz bandwidth of a channel, the image's vertical resolution was reduced from 525 lines to 405. The vertical resolution was 77% of monochrome, and the horizontal resolution was 54% of monochrome.

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