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discovered by Ducos de Hauron in 1869, which consists in splitting up the image into the three fundamental colours of the spectrum, red, green and violet, and afterwards in re-composing it.
But while, in the case of coloured plates, the analysis and synthesis of colours is produced automatically on the same stand, in the three-colour process the two operations are completely separated.
In colour cinematography it is precisely the three-colour system proper that has been applied; and with the improvements which are certainly bound to be introduced, it will lead to completely practical results. It may be said that no substantial change has been made in the three-colour process since the time of its discovery as regards the analysis of colours; this operation has merely benefited much by the great improvements that have been realized in chromatic sensitiveness.
The apparatuses which have been devised for producing the three-colour selection are innumerable; the mechanical and optical characteristics required in apparatuses for the production of fixed images are somewhat different from those necessary in cinematographic cameras. With regard to the former, the use of plates has made possible the construction of apparatuses, which by only one exposure, or by three exposures in very rapid succession can produce the three selected negatives through the three corresponding red, green and violet filters. A typical example of this method is employed in the camera invented by Prof. Miethe as far back as 1900, an improved model of which is to-day constructed by the Uvachrome Company of Munich. With this camera the Uvachrome Co. took the very large number of colour photographs of monuments and paintings which appeared in the fine volume Roma Sacra, published in 1927, on the occasion of the Holy Year celebrations.
Other cameras fitted with only one lens, permit the taking of photographs with only one exposure, which allows of a greater speed.
These cameras are based on the use of semi-transparent mirrors combined with light filters for selection. They are, however „