Trichromia (from Greek: tri = three and chromos = color) is a color photography procedure in which three separate black and white images are combined by projection into three colors by applying three color filters (red, green and blue) overlap.
The combination of the three images to 1 image is done via the "classic" black and white film methods. By developing a positive of each of the black and white negatives and then capturing the three images by projection through the color filters on a color film, the color image is created. The colors can also be created by electronic or digital method (with a PC, for example, with photo editing software).
The difference between trichromia and today's color shots consists in the fact that the three separate black and white images are photographed sequentially and not later mounted to a color image.
The method has been in use since the end of the 19th century and was only possible when black and white material could be transferred to color sensitive photo paper. Also see
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