Editing Exposure (photography) (section)

==Optimum exposure==
{{main article|sensitometry}}

"Correct" exposure may be defined as an exposure that achieves the effect the photographer intended.<ref>Peterson, Bryan, "Understanding Exposure", 2004, {{ISBN|0-8174-6300-3}} : p.14</ref>

A more technical approach recognises that a photographic film (or sensor) has a physically limited [[sensitometry|useful exposure range]],<ref>Ray, S.F. et al. 2000 "The Manual of Photography" Focal Press, {{ISBN|0-240-51574-9}}, p.230</ref> sometimes called its [[dynamic range]].<ref>Ray, S.F. et al. 2000 "The Manual of Photography" Focal Press, {{ISBN|0-240-51574-9}}, p.121 and p.245</ref> If, for any part of the photograph, the actual exposure is outside this range, the film cannot record it accurately. In a very simple model, for example, out-of-range values would be recorded as "black" (underexposed) or "white" (overexposed) rather than the precisely graduated shades of colour and tone required to describe "detail". Therefore, the purpose of exposure adjustment (and/or lighting adjustment) is to control the physical amount of light from the subject that is allowed to fall on the film, so that 'significant' areas of shadow and highlight detail do not exceed the film's useful exposure range. This ensures that no 'significant' information is lost during capture.

The photographer may carefully overexpose or underexpose the photograph to ''eliminate'' "insignificant" or "unwanted" detail; to make, for example, a white altar cloth appear immaculately clean, or to emulate the heavy, pitiless shadows of [[film noir]]. However, it is technically much easier to discard recorded information during [[image processing|post processing]] than to try to 're-create' unrecorded information.

In a scene with strong or harsh lighting, the ''ratio'' between highlight and shadow luminance values may well be larger than the ''ratio'' between the film's maximum and minimum useful exposure values. In this case, adjusting the camera's exposure settings (which only applies changes to the whole image, not selectively to parts of the image) only allows the photographer to choose between underexposed shadows or overexposed highlights; it cannot bring both into the useful exposure range at the same time. Methods for dealing with this situation include: using what is called [[fill light]]ing to increase the illumination in shadow areas; using a [[graduated neutral-density filter]], flag, scrim, or [[gobo (lighting)|gobo]] to reduce the illumination falling upon areas deemed too bright; or varying the exposure between multiple, otherwise identical, photographs ([[exposure bracketing]]) and then combining them afterwards in an [[High-dynamic-range imaging|HDRI]] process.

===Overexposure and underexposure===
{{Redirect|Underexposure|the 2005 film by Oday Rasheed|Underexposure (film)}} <!-- [[Overexposure]] redirects here too. -->
[[File:Stühle Froschperspektive.jpg|thumb|White chair: Deliberate use of overexposure for aesthetic purposes]]

A photograph may be described as ''overexposed'' when it has a loss of highlight detail, that is, when important bright parts of an image are "washed out" or effectively all white, known as "blown-out highlights" or "[[Clipping (photography)|clipped whites]]".<ref>{{cite web | url = http://www.illustratedphotography.com/basic-photography/iso-and-film-speed | title = Basic Photography&nbsp;— ISO and Film Speed | author = Ed van der walt | access-date = 2 July 2011}}</ref>  A photograph may be described as ''underexposed'' when it has a loss of shadow detail, that is, when important dark areas are "muddy" or indistinguishable from black,<ref>{{cite book | title = Digital Photography: Top 100 Simplified Tips & Tricks | edition = 4th | author = Rob Sheppard | publisher = John Wiley and Sons | date = 2010 | isbn = 978-0-470-59710-1 | page = 40 | url = https://books.google.com/books?id=3M0CZb4dFSgC&pg=PA40 }}</ref> known as "blocked-up shadows" (or sometimes "crushed shadows", "crushed blacks", or "clipped blacks", especially in video).<ref>{{cite book | title = Illustrated Dictionary of Photography | author = Barbara A. Lynch-Johnt | author2 = Michelle Perkins | name-list-style = amp | publisher = Amherst Media | date = 2008 | isbn = 978-1-58428-222-8 | page = [https://archive.org/details/Illustrated_Dictionary_of_Photography_2008/page/n15 15] | url = https://archive.org/details/Illustrated_Dictionary_of_Photography_2008 | quote = blocked-up shadows crushed. }}</ref><ref>{{cite book | title = Color Correction for Digital Video | author = Steve Hullfish | author2 = Jaime Fowler | name-list-style = amp | publisher = Focal Press | date = 2005 | isbn = 978-1-57820-201-0 | pages = 135–136 | url = https://books.google.com/books?id=s3rQjdG2pBUC&q=crushed+shadows+blocked-up+blacks&pg=PA135}}</ref><ref>{{cite book | title = Lighting for Digital Video & Television | author = John Jackman | publisher = Focal Press | date = 2004 | isbn = 978-1-57820-251-5 | page = 60 | url = https://books.google.com/books?id=u1C4aZmMeTUC&q=crushed-blacks+highlights&pg=PA60}}</ref> As the adjacent image shows, these terms are technical ones rather than artistic judgments; an overexposed or underexposed image may be "correct" in the sense that it provides the effect that the photographer intended. [[Exposure_compensation|Intentionally over- or underexposing]] (relative to a standard or the camera's automatic exposure) is casually referred to as "[[exposing to the right]]" or "exposing to the left" respectively, as these shift the histogram of the image to the right or left.