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Proceedings Paper

Improving the sensitometric and OECF standards: recognizing the photosensitive exposure range
Author(s): Michael G. Prais
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Paper Abstract

This article demonstrates that and how sensitometric and opto-electronic characteristic function (OECF) standards should be changed: The sensitivity S of all photosensitive arrays is--and, in standards, should be--determined by the midtone photosensitive exposure of the array Hmid, the binary logarithm of which is [log2(Hmax) + log2(Hmin)]/2. The reference exposure Ho = S/Hsp of a photosensitive array is--and, in standards, should be--determined by the width of the photosensitive exposure range Δ, which is determined by the measured minimum and maximum usable photosensitive exposures, Hmax and Hmin. Knowledge of Hmax and Hmin (or Hmid and Δ) makes the reference exposure Ho, the speed point exposure Hsp and the safety factor σ unnecessary, and these extraneous quantities should be eliminated from the sensitometric standards. In addition, the sensitometric standard for solid-state arrays, ISO 12232-2006, and the OECF standard, ISO 14524-1999, should be changed because they use a photosensitive exposure range which is inappropriate for solid-state arrays. Finally, this article shows that all current standards establish midtone reflectances Rmid for standard photosensitive arrays that are much less than oft-touted 18% making most references to 18% inappropriate.

Paper Details

Date Published: 24 January 2011
PDF: 11 pages
Proc. SPIE 7876, Digital Photography VII, 78760T (24 January 2011); doi: 10.1117/12.871549
Show Author Affiliations
Michael G. Prais, Consultant (United States)


Published in SPIE Proceedings Vol. 7876:
Digital Photography VII
Francisco H. Imai; Feng Xiao, Editor(s)

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