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8 History of Three-Color Photography
prevented from experimenting by the fact that he did not return till 1866, and that then the Austro-Prussian war broke out.
We have now to return to du Hauron. In November, 1868, he applied for a French patent, No. 83,061, entitled "Les Couleurs en Photographie, Solution du Probleme." In the following year a series of articles was published in Le Gers, in Auch, under the same title, and a letter was addressed to the Societe franchise de Photographie, which was read at the meeting of May 7, and summarized by A. Davanne.14 These articles were elaborated and published in book form,15 and on examination of the arguments it will be found that du Hauron's methods were in close accord with the most successful of present day practice. His idea was to isolate each printing color so that it would, in the final print, properly represent the varying ratios of that color in the subject, and this is quite clear from his definition of the colors of his filters.
Chas. Cros. — At this time Chas. Cros published in Les Mondes, Feb. 25, 1869,16 an article entitled: "Solution du Probleme de la Photographie des Couleurs/' which was subsequently printed in pamphlet form. Cros first explained that he had neither the means for carrying out his ideas, nor the desire for commercial exploitation, being content merely with the honor of his discovery. He defined the three elementary colors as red, yellow and blue and suggested the taking of separation negatives, each representing one of these three colors. He outlined two methods of analysis,— successive and simultaneous. The first was to be carried out by the use of three filters, such as glass coated with colored varnishes or cells holding colored liquids. Simultaneous analysis was to be effected by the use of a prism, which should send only red, yellow and blue light into the camera, thus meaning probably the use of a prism in front of or behind the lens, and anticipating the dispersion processes of Drac and others. He also suggested for portraiture and still life the illumination of the subject with colored lights.
For the synthesis he outlined most clearly the optical superposition of the colored images as in the chromoscope (see also p. 109), and also the synthesis by persistence of vision by the aid of the phenakistoscope or zoetrope. He also defined the superposition of colored impressions, and although he first suggested the use of red, green and violet inks, he stated that probably red, yellow and blue would be better.
The Theoretical Basis of Tri-Color Photography. — Whilst du Hauron and Cros did not have all the instrumental advantages that we now have, yet they laid down in somewhat precise terms the fundamental basis of three-color photography by subtractive processes, that is to say, the printing colors should be anti-chromatic to the taking colors. Color curve analysis was merely introduced at a later date, and for some time acted upon the wheels of progress as a drag. Fortunately with better instrumental means and a clearer grasp of the essential