The Keller-Dorian process was an additive color process invented and patented by the French physicist Rodolphe Berthon in 1908. His invention was directly inspired by Gabriel Lippmann’s work on “integral photography” – a relief film process which involved embossing film with lenticular elements. Berthon adapted Lippmann’s idea for color cinematography.

This process allowed color information to be captured on a B/W emulsion, the colors were then revealed in projection using a trichrome filter. The lenticular process can be considered as a screen process, but the array is formed entirely by optical means. A red, green and blue three-banded filter was placed in the lens system, and the screen image was formed by microscopic optical elements engraved on the film base. When the principle was unveiled, most specialists considered it the most elegant solution to the problem of color motion pictures so far discovered. 

In 1913, Berthon, who had acquired a certain notoriety, was hired by Charles Pathé as a research engineer. This was an opportunity for him to undertake the development of a film embossing machine and to carry out research on the panchromatization of the film (sensitizing B/W emulsion to the full visible spectrum). The reports he wrote were subsequently used by Pathé to file a patent in the name of his company, without including Berthon’s name on the patent. Feeling cheated, Berthon left the Pathé company in March 1914.

The First World War interrupted further research into the technology in France. After the war, Berthon was in search of practical, scalable solutions and joined forces with the industrialist, Albert Keller-Dorian who ran a custom fabric engraving plant in Mulhouse and in Lyon. Keller-Dorian’s curiosity for photographic technology led him to move in scientific circles, where he came into contact with Berthon and his invention and began work on devising the technology for an embossing machine that would constitute the foundation of the lenticular process. In 1924, some test footage was shown, but the problems associated with making prints of reliable quality were far from being resolved. Soon after the founding of ‘La Société du Film en couleurs Keller-Dorian’ in 1924, Albert Keller-Dorian died and a serious disagreement occurred between the shareholders – who were demanding immediate results – and the research team, who considered that the process was not yet ready to be commercialized. By this time Berthon had been sidelined, and it was Professor Henri Chrétien who was leading the research, but he soon resigned in protest. His departure interrupted any further serious progress.

Eastman Kodak, developing an interest in the process, sent over its engineering consultant, Raymond Edwin Crowther from the US. Kodak acquired the patent for 16mm and launched Kodacolor in 1928, which was well suited to the amateur market. The reversal film enabled direct projections without having to make prints. And later, in the early 1930s, after Berthon's original 1909 patent had fallen into the public domain, the German company Agfa took out a similar patent under the trademark of Agfacolor, also with the intent of bringing color to the 16mm amateur market. 

In the UK, Louis Blattner, who was involved in research on magnetic sound recording, became interested in the Keller-Dorian process and bought the rights for Great Britain in 1929. The process, renamed Moviecolor, was short-lived, because Eastman Kodak refused to supply him with embossed film, and Blattner sold back the rights a year later.

In 1930, the French company (Société française de cinématographie et de photographie en couleurs Keller-Dorian) was declared insolvent and the patents were purchased by William Celestin at the head of an Anglo-American group under the name of ‘Keller-Dorian Colorfilm of America’. Kodak, Technicolor and Paramount acquired several patents and conducted research to deal with the problem of producing prints at an industrial scale. After the purchase of these patents, the activity of the French color film company Keller-Dorian was put on hold.

At the same time, Berthon founded a new rival company, La Cinéchromatique, and continued his research into the problem of making prints. But the funds at his disposal were very limited. Berthon entered into a partnership with the Kyslin Corporation, to exploit his patents in the US. Additions to the Berthon’s patents were filed by Kyslin and research engineer Carl Gregory but the project was not commercially developed.

In 1931, the Siemens-Halske German trust purchased the La Cinéchromatique patents. After four years of research, company engineers succeeded in making good-quality embossed prints. In 1936, the first German fiction color film, Das Schönheitsfleckchen (The Beauty Spot) was shown in Berlin during the Olympic games and the film made a notable international impact.

In 1938, Agfa developed Pantachrom, a bipack lenticular process, but Agfa’s own parallel advances in a subtractive monopack film led to the rapid demise of lenticular film development in Germany. Both Agfa and Siemens-Halske had withdrawn from further lenticular development by the end of 1938.

In the early 1930s, the French company Thomson-Houston had undertaken research and shot test footage without much to show for their efforts, then all activity ceased due to the advent of the Second World War. After the Liberation, Thomson-Houston made a new attempt to relaunch its Thomsoncolor process, announcing in 1947 that Jacques Tati’s Jour de Fête was to be its first color production. But the Thomsoncolor printing process failed and the film was eventually distributed only in a B/W version.

In the 1950s, the lenticular process made one last comeback with Eastman Embossed Color Kinescope Recording film, type 5209, used to record color television programs. This technology made it possible to record live shows at a stage when magnetic videotape recording was still only an experimental technology.

The Keller-Dorian process, although based on an elegant and promising idea, never got beyond the experimental stage. It was another 80 years before Lippmann’s work on micro-lenses was to arouse interest again – leading to technology used today in domains as varied as astronomy, holography and fiber optics. While the Bayer matrices used in digital camera sensors (charge-coupled devices, or CCDs) are based on the same underlying principles of lenticular pattern processes.