Additive and Subtractive Colour Photography – Part 3 of 5

Submitted by Al …

Adapted from The Encyclopedia of Photography ©1963

ADDITIVE COLOUR PROCESS (continued)

Other processes which employed regular patterns of lines or squares were the Thames Plate (1906), the Finlay Plate (1907), and the Dufaycolor Plate. 

Techniques employed by Dufay Limited, produced collodion-coated plates having approximately 1,000,000 colour filter elements per square inch. The Dufaycolor Plate, like the Agfacolor and Autochrome Plates, had the sensitized emulsion coated in contact with the screen, while the other processes, such as Finlay, had separate screen plates which required careful registration with the photograph. 

It is interesting to note that colour television today is the most important application of the mosaic process. The RCA system, for example, consists of a picture tube having the inner surface or screen coated with 250,000 dots each of red, green, and blue phosphors. These dots emit light when excited by a beam of electrons from the red, green, and blue electron guns. Located between the guns and the screen is a metal plate containing 250,000 holes. When the red gun is operating, the electrons passing through the holes in the place can only strike the red dots, thus forming a red image. The green and blue guns function in a similar manner, and the firing of all three guns produces three colour images which merge into a full colour image.

Lenticular Process

A variation of the screen method was patented by Rodolphe Berthon in 1909. It used a film which was embossed on the base side with tiny lenses or lenticulations and emulsion-coated on the other side. The camera lens was coated with strips of red, green, and blue filters. Since the lenticulations faced the lens, light from the subject passed through the camera lens and to the lenticulated surface. The curvature of each lenticule then produced tiny images of the three filters on the emulsion surface. 

After development by reversal, the film was projected with red, green, and blue filter strips over the projection lens.

A process of this type was marketed in 1928 by the Eastman Kodak Company as a 16mm motion-picture film. Although it enjoyed considerable success, it ceased to be commercially important with the advent of Kodachrome Film in 1935.

In part four of our series, we will explore the subtractive colour process.