The Kodachrome process was invented in 1913 by John G. Capstaff for still photography and subsequently adapted to motion pictures. For the process two frames were advanced simultaneously, one located above the other. The light passed either through two lenses or through a beam-splitter, fitted with red and green filters. The release print was exposed through a beam-splitter whereby the alternate frames were projected onto either side of double-coated stock. After development by a usual b/w process, the film was tanned to harden the exposed areas. The soft areas were dyed red-orange and blue-green respectively.
During the capturing of the film a beam-splitter in combination with filters in the camera divided the incoming light into a red and a green separation negative on black-and-white stock. When projected in the cinema the two images were combined simultaneously by additive mixture through corresponding red and green filters into one picture consisting of red and green colored light. The reduction of the whole color range to two colors (and their additive combinations) was necessary because of the complex optical arrangement.
The first subtractive 2 color process introduced by Technicolor captured the incoming light through a beam splitter with red and green filters also. However, in contrast to the first Technicolor process, the two b/w images were recorded on one negative strip. This was achieved by the pull-down of two frames simultaneously, a process that required the double speed in the camera. These two frames were arranged in pairs, whereby the green record was inverted up-side down (see image).
The third Technicolor process used the same camera as process no. II to combine a pair of frames of the red and green record respectively on the b/w negative (see image). In contrast to the former process, however, the two images were printed on one side of the positive by the dye transfer or imbibition process.