In bipack color photography for motion pictures, two strips of black-and-white 35 mm film, running through the camera emulsion to emulsion, are used to record two regions of the color spectrum, for the purpose of ultimately printing the images, in complementary colors, superimposed on one strip of film. The result is a multicolored projection print that reproduces a useful but limited range of color by the subtractive color method. Bipack processes became commercially practical in the early 1910s when Kodak introduced duplitized film print stock, which facilitated making two-color prints.[1]
Bipack photography was, from about 1935 to 1950, the most economical means of 35 mm natural color cinematography available, used when color was wanted but the budget could not bear the much higher cost of three-strip Technicolor or the less well-known alternative three-color processes sometimes available outside the US. After 1950, when economical "monopack" color negative and print stocks such as Eastmancolor and Ansco Color were introduced, the use of bipack photography and printing rapidly declined. By 1955 all two-color motion picture processes were commercially extinct in the US.
Bipack and three-element tripack sandwiches of plates and films were used in some early color processes for still photography, the field in which the concept originated.