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sensitometry
Sensitometry is the scientific study of light-sensitive materials, especially photographic film. The study has its origins in the work by Ferdinand Hurter and Vero Charles Driffield (circa 1876) with early black-and-white emulsions.〔Hurter, Ferdinand & Driffield, Vero Charles (1890) ''Photochemical Investigations and a New Method of Determination of the Sensitiveness of Photographic Plates'', J. Soc. Chem. Ind. May 31, 1890.〕 They determined how the density of silver produced varied with the amount of light received, and the method and time of development.
== Details ==
Plots of film density (log of opacity) versus the log of exposure are called characteristic curves,〔 Hurter–Driffield curves,〔 H–D curves, HD curves, H & D curves, D–logE curves, or D–logH curves. The overall shape is a bit like an "S" slanted so that its base and top are horizontal. There is usually a central region of the HD curve which approximates to a straight line, called the "linear" or "straight-line" portion; the slope of this region is called the gamma. The low end is called the "toe", and at the top, the curve rounds over to form the "shoulder".
Different commercial film materials cover a gamma range from about 0.5 to about 5. Often it is not the original film that one views but a second or later generation. In these cases the end-to-end gamma is approximately the product of the separate gammas. Photographic paper prints have end-to-end gammas generally somewhat over 1. Projection transparencies for dark surround viewing have end-to-end gamma approximately 1.5. A full set of HD curves for a film shows how these vary with developer type and time.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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