Editing Exposure (photography) (section)

==Definitions==

===Radiant exposure===
'''Radiant exposure''' of a ''surface'',<ref>{{cite book | title = Introduction to Color Imaging Science | author = Hsien-Che Lee | publisher = Cambridge University Press | date = 2005 | isbn = 978-0-521-84388-1 | page = 57 | url = https://www.cambridge.org/core/books/introduction-to-color-imaging-science/ACD65575EE981E895EE8C92576918723}}</ref>
denoted ''H''<sub>e</sub> ("e" for "energetic", to avoid confusion with [[Photometry (optics)|photometric]] quantities) and measured in {{nobreak|J/m<sup>2</sup>}}, is given by<ref>
{{cite book | title = Silver-halide Recording Materials | author = Hans I. Bjelkhagen | publisher = Springer | date = 1995 | isbn = 978-3-540-58619-7 | page = 15 | url = https://books.google.com/books?id=tiGP9MrVs90C&q=exposure+radiometric+photography&pg=PA15}}</ref>
:<math>H_\mathrm{e} = E_\mathrm{e}t,</math>
where
*''E''<sub>e</sub> is the [[irradiance]] of the surface, measured in {{nobreak|W/m<sup>2</sup>}};
*''t'' is the [[exposure duration]], measured in s.

===Luminous exposure===
'''Luminous exposure''' of a ''surface'',<ref>National Institute of Standards and Technology [http://physics.nist.gov/Divisions/Div844/facilities/photo/Flash/flash.html] {{Webarchive|url=https://web.archive.org/web/20090118125052/http://www.physics.nist.gov/Divisions/Div844/facilities/photo/Flash/flash.html|date=2009-01-18}}. Retrieved Feb 2009.</ref> denoted ''H''<sub>v</sub> ("v" for "visual", to avoid confusion with [[Spectrophotometry|radiometric]] quantities) and measured in {{nobreak|lx⋅s}}, is given by<ref name=attridge>
{{cite book | title = The Manual of Photography: Photographic and Digital Imaging | edition = 9th | chapter = Sensitometry | author = Geoffrey G. Attridge | editor = Ralph E. Jacobson | editor2 = Sidney F. Ray | editor3 = Geoffrey G. Attridge | editor4 = Norman R. Axford | publisher = Oxford: Focal Press | date = 2000 | isbn = 0-240-51574-9 | pages = 218–223 | chapter-url = https://books.google.com/books?id=MblHnLN2N2kC&q=intitle:manual+sensitometry+exposure+illuminance+time+lux&pg=PA218}}</ref>
:<math>H_\mathrm{v} = E_\mathrm{v}t,</math>
where
*''E''<sub>v</sub> is the [[illuminance]] of the surface, measured in lx;
*''t'' is the exposure duration, measured in s.

If the measurement is adjusted to account only for light that reacts with the photo-sensitive surface, that is, weighted by the appropriate [[spectral sensitivity]], the exposure is still measured in radiometric units (joules per square meter), rather than photometric units (weighted by the nominal sensitivity of the human eye).<ref>
{{cite book | title = Physical Principles of Remote Sensing | author = Gareth Rees | publisher = Cambridge University Press | date = 2001 | isbn = 978-0-521-66948-1 | page = [https://archive.org/details/physicalprincipl0000rees_f1n5/page/114 114] | url = https://archive.org/details/physicalprincipl0000rees_f1n5 | url-access = registration | quote = film photometric radiometric spectral-sensitivity exposure. }}</ref> Only in this appropriately weighted case does the ''H'' measure the effective amount of light falling on the film, such that the [[Hurter–Driffield curve|characteristic curve]] will be correct independent of the spectrum of the light.

Many photographic materials are also sensitive to "invisible" light, which can be a nuisance (see [[UV filter]] and [[IR filter]]), or a benefit (see [[infrared photography]] and [[full-spectrum photography]]). The use of radiometric units is appropriate to characterize such sensitivity to invisible light.

In [[sensitometric]] data, such as characteristic curves, the ''log exposure''<ref name=attridge/> is conventionally expressed as log<sub>10</sub>(''H''<!-- TBD: or ''H''<sub>v</sub>? -->). Photographers more familiar with base-2 logarithmic scales (such as [[exposure value]]s) can convert using {{nowrap|log<sub>2</sub>(''H''<!-- TBD: or ''H''<sub>v</sub>? -->) ≈ 3.32 log<sub>10</sub>(''H''<!-- TBD: or ''H''<sub>v</sub>? -->)}}.

{{SI_radiometry_units|2|self|nb}}<!-- Optional parameter is table number -->

{{SI_light_units|1|self|nb}}<!-- Optional parameter is table number -->