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. They determined how the density of silver produced varied with the amount of light received, and the method and time of development.
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.
See also 
- Film speed
- Leon Warnerke aka Władysław Małachowski, inventor of the first practical sensitometer in 1880.
- Hurter and Driffield
- Julius Scheiner - Scheiner sensitometer
- Henry Chapman Jones - Chapman Jones plate tester
- Josef Maria Eder and Walter Hecht (de) - Eder-Hecht neutral wedge sensitometer
- Spectral sensitivity
- Zone system
- 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.
- "KODAK PROFESSIONAL TRI-X 320 and 400 Films" (PDF). Eastman Kodak Company. May 2007.
- Stuart B. Palmer and Mircea S. Rogalski (1996). Advanced University Physics. Taylor & Francis. ISBN 2-88449-065-5.
- Kenneth W. Busch and Marianna A. Busch (1990). Multielement Detection Systems for Spectrochemical Analysis. Wiley-Interscience. ISBN 0-471-81974-3.
- Richard R. Carlton, Arlene McKenna Adler (2000). Principles of Radiographic Imaging: An Art and a Science. Thomson Delmar Learning. ISBN 0-7668-1300-2.
- Ravi P. Gupta (2003). Remote Sensing Geology. Springer. ISBN 3-540-43185-3.
- Leslie D. Stroebel and Richard D. Zakia (1993). The Focal Encyclopedia of Photography. Focal Press. ISBN 0-240-51417-3.
- Basic Sensitometry And Characteristics of Film (Kodak undated)
- A memorial volume containing an account of the photographic researches of Ferdinand Hurter & Vero C. Driffield ; being a reprint of their published papers, together with a history of their early work and a bibliography of later work on the same subject. (Royal Photographic Society of Great Britain 1920)
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