Louis Dufay was a French inventor who took the principles of the autochrome process and improved on them by coating a glass plate with a much more regular-shaped pattern than the autochrome’s method of scattering coloured potato starch filters at random. Dufay’s method was to superimpose pairs of lines consisting of complementary colours such as magenta and green at right angles on a screen of pairs of non-complimentary colours such as cyan and yellow. Dufay claimed this actually offered four colours since the combination of green and cyan produced a different colour to the combination of green and yellow. In this way the screen contained up to 200 elements to the inch. Originally called Diopticolore, but then Dioptichrome, Dufay introduced the process in 1909.

 

The method of exposure was to place a monochrome plate in a frame behind a dioptichrome screen, make the exposure, process it by reversal development to make a positive and then put the resulting image back into the frame with the screen through which it had originally been exposed. It could then be viewed as a colour picture. In 1910 a new version was introduced that used an integral screen coated with the required emulsion.

 

A dioptichrome screen transmitted 21 per cent of the light falling on it. Consequently a dioptichrome plate required a shorter exposure than an autochrome, something like one second at f/11 in bright sunlight. Dioptichromes remained on the market until the outbreak of the First World War, and Louis Dufay went on to adapt his methods for use with flexible film. The result was Dufaycolor.