Trichrome Photography

Trichrome photography involves taking three exposures of the same subject on black and white film. Each exposure is taken through a red, green or blue filter. These photos are then combined to produce a colour image. Three separate exposures could be taken with the same camera mounted on a tripod, though this would only be possible for static subjects, a purpose made camera with three lenses allows the 3 exposures to be made simultaneously.
One of the early users of the process, over a hundred years ago, was Sergey Prokudin-Gorsky , he used projectors with coloured filters to make a combined image, nowadays it can be done with photo editing software such as Photoshop.