Effect of the Photographic Gamma on the Luminance of Hologram Reconstructions*

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Abstract
An expression derived for hologram exposures made along the straight-line portion of the H-D curve of a photographic plate shows that the relationship between the luminance of the reconstructed hologram image and the luminance of the original object depends on the value and sign of the gamma of the photographic processes.To check the theory, several holograms of different exposures were superimposed on Kodak 649-F plates that were pre-flashed with a uniform illuminance so the H-D curve of the photographic process is straight. The calculated and measured luminance ratios of the different reconstructions agree within experimental error. Since the gamma of the usual photographic process is positive, instead of negative, even if the gamma of the photographic process is equal to 2, it is not valid to assume that the relative luminance of the reconstruction of a given superimposed hologram is proportional to the product of the exposure due to the object beam and the exposure due to the reference beam used in the making of the hologram. This assumption would be valid for all fringe contrasts only if gamma were -2.

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