People have been looking for means of recovering underdeveloped images since the inception of photography. The use of two partially reflective parallel mirrors on either side of the negative is one of the more simple possabilities. This system has been investigated to see how much contrast enhancement it provides and what affect it has on resolution and graininess. It has been found that contrast gains of 1.5 to about 3.0 times can be expected for images with densities from .14 to .30. Also the resolution of low contrast images is increased slightly and graininess is decreased by almost three times. However, the effectiveness of the system does seem to be limited to very low density images.
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School of Photographic Arts and Sciences (CIAS)
Boden, Dudley, "Image Quality of a Multiple-Pass Optical Contrast Enhancement Technique" (1978). Thesis. Rochester Institute of Technology. Accessed from
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