The Kromskop was an early optical viewing instrument invented by the American photographer and inventor Frederic Eugene Ives in 1892, designed to synthesise and display full colour photographic images at a time when no practical method of directly capturing colour photographs existed. It represented one of the most sophisticated and visually convincing demonstrations of colour photography available in the late nineteenth century, and attracted considerable scientific and public interest during the period.
The device worked on the principles of additive colour synthesis, using a carefully arranged system of semi-silvered mirrors, fully silvered mirrors, and coloured filters in red, green, and blue to simultaneously combine three separate monochrome transparencies - known as separation negatives or separation positives - into a single unified full colour image as seen by the viewer. Each of the three monochrome transparencies had been captured through a correspondingly coloured filter at the time of photography, recording the red, green, and blue colour information of the original scene separately on three individual black and white emulsions.
When the three transparencies were loaded into the Kromskop and illuminated from behind, the optical system of mirrors and filters recombined the red, green, and blue filtered images in precise alignment and superimposed them on top of one another in the viewer's eye, recreating the full colour appearance of the original scene through the additive mixing of the three primary colours of light. The result, when the transparencies were well made and correctly aligned, was a remarkably convincing and richly coloured image that astonished contemporary viewers accustomed only to monochrome photography.
Ives marketed the Kromskop commercially in both a single viewer version for individual use and a larger projection version - the Kromskop projector - capable of displaying the combined colour image to an audience. He also produced sets of pre-made colour transparencies, which he called Kromograms, that could be purchased and viewed in the instrument. Despite the quality of the colour images it produced, the Kromskop never achieved widespread commercial success, largely due to the complexity and cost of producing the matched sets of separation transparencies required, the cumbersome nature of the viewing apparatus itself, and the eventual development of more practical single plate colour photographic processes that made the separation negative approach obsolete.
Nevertheless, the Kromskop occupies an important place in the history of colour photography as one of the earliest practical demonstrations of additive colour synthesis applied to photographic imaging, anticipating the principles that would later underpin colour film, colour television, and modern digital display technology.