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.

Plots of film density (log of opacity) versus the log of exposure are called characteristic curves, Hurter–Driffield curves, H–D curves,cite book | title = Advanced University Physics | author = Stuart B. Palmer and Mircea S. Rogalski | publisher = Taylor & Francis | year = 1996 | ibsn = 2884490655 | url = http://books.google.com/books?id=TF6Igz5lJLgC&pg=PA349&dq=hurter-driffield-curve+h-d-curve&lr=&as_brr=3&ei=songR5KAJIWusgOWlPQU&sig=FgC6_uAklssPUpNaUyyr2lS0hNk ] HD curves, [cite book | title = Multielement Detection Systems for Spectrochemical Analysis | author = Kenneth W. Busch and Marianna A. Busch | publisher = Wiley-Interscience | year = 1990 | ibsn = 0471819743 | url = http://books.google.com/books?id=9H0W1J-Rku4C&pg=PA339&dq=h-d-curve+density&lr=&as_brr=3&ei=qYzgR46lBYbosQOrzpgV&sig=_kTikTsCw2-7B8XvfO6y73rmTkc#PPA341,M1 ] H & D curves, [cite book | title = Principles of Radiographic Imaging: An Art and a Science | author = Richard R. Carlton, Arlene McKenna Adler | publisher = Thomson Delmar Learning | year = 2000 | ibsn = 0766813002 | url = http://books.google.com/books?id=oA-eBHsapX8C&pg=PA318&dq=h%26d-curve+density&lr=&as_brr=3&ei=to3gR5GCLI6eswOs98kV&sig=s_vE4f5PMysrrCtgM7_HJrsRu_Y ] D–logE curves, [cite book | title = Remote Sensing Geology | author = Ravi P. Gupta | publisher = Springer | year = 2003 | ibsn = 3540431853 | url = http://books.google.com/books?id=74T8X1zqgF4C&pg=PA62&dq=d-log-e-curve+density&lr=&as_brr=3&ei=eY7gR4qWEILusgO60YCrAg&sig=MBImrU6KwlZwoV29Xl1PywwEINQ ] or D–logH curves. [cite book | title = The Focal Encyclopedia of Photography | author = Leslie D. Stroebel and Richard D. Zakia | publisher = Focal Press | year = 1993 | ibsn = 0240514173 | url = http://books.google.com/books?id=CU7-2ZLGFpYC&pg=PA794&dq=d-log-h-curve+density&lr=&as_brr=3&ei=BI_gR6qIGIiUtgOY5tEV&sig=wfoH3l-C-AKifDLLObbnYn7FrHg ] 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".

Usable values of gamma are typically between 0.8 and 1.2. (But values of up to 1.5 may be useful for slides). A full set of HD curves for a film shows how these vary with developer type and time.cite web | url = http://www.kodak.com/global/en/professional/support/techPubs/f4017/f4017.jhtml | title = KODAK PROFESSIONAL TRI-X 400 Film / 400TX | Kokak Professional Support]

References

ee also

* Densitometry
* Hurter and Driffield