Autochromes Lumière

Additive synthesis

The Optical Mixture of Blue, Green and Red
The additive synthesis of colour rests on an optical mixture of the three primary colours: blue, green, and red. Or alternately, violet, green and orange when it is a matter of the three colours used in systems such as the Authochrome.

This trichromatic method covers the systems which permit the reconstitution of all the colours by superposition of primary-coloured lights (e.g., a video projection) or by the juxtaposition of coloured micro-surfaces (e.g., the Autochrome, as well as television screens and monitors). In the latter case, the synthesis of colour exploits the phenomena of retinal confusion, resulting from the small size of the coloured elements. These minuscule coloured elements cannot be perceived individually by the visual sensors distributed on the surface of the retina. The optic nerves transmit impulses to the brain which translates this colour information, where they are added together to represent the colours that result from this association.

This manner of reconstruction is not to be confused with subtractive synthesis, which exploits a different triad of primary colours: yellow, red and blue. The equivalent colours for photographic applications are: yellow, magenta and cyan. These are made available in superimposed and transparent layers. Each coloured layer cuts out the part of the energy corresponding to the spectrum of absorption from white light.