Farbefotografie

SUBJECT AREA: Photography, film and optics

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A man of considerable intellect, Cros occupied himself with studies of topics as diverse as Sanskrit and the synthesis of precious stones. He was in particular interested in the possibility of colour photography, and deposited an account of his theories in a sealed envelope with the Académie des Sciences on 2 December 1867, with instructions that it should be opened in 1876. Learning of a forthcoming presentation on colour photography by Ducos du Hauron at the Société Française de Photographie, he arranged for the contents of his communication to be published on 25 February 1869 in Les Mondes. At the Société's meeting on 7 May 1869, Cros's letter was read and samples of colour photography from Ducos du Hauron were shown. Both had arrived at similar conclusions: that colour photography was possible with the analysis of colours using negatives exposed through red, green and blue filters, as demonstrated by Clerk Maxwell in 1861. These records could be reproduced by combining positive images produced in blue-green, magenta and yellow pigments or dyes. Cros and Ducos du Hauron had discovered the principle of subtractive colour photography, which is used in the late twentieth century. In 1878 Cros designed the Chromometre, a device for measuring colours by mixing red, green and blue light, and described the device in a paper to the Société Française de Photographie on 10 January 1879. With suitable modification, the device could be used as a viewer for colour photographs, combining red, green and blue positives. In 1880 he patented the principle of imbibition printing, in which dye taken up by a gelatine relief image could be transferred to another support. This principle, which he called hydrotypie, readily made possible the production of three-colour subtractive photographic prints.

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