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'''Exchangeable image file format''' (official abbreviation '''Exif''', not '''EXIF''') is a specification for the [[image]] [[file format]] used by [[digital camera]]s. It was created by the [[Japan Electronic Industry Development Association]] ([[JEIDA]]). The specification uses the existing
Version 2.1 of the specification is dated [[June 12]], [[1998]] and version 2.2 is dated April [[2002]].
The Exif tag strucure is taken from that of TIFF files. There is a large overlap between the tags defined in the [[Tagged Image File Format|TIFF]], Exif, [[Tag Image File Format / Electronic Photography|TIFF/EP]] and [[Design rule for Camera File system|DCF]] standards.
The metadata tags defined in the Exif standard cover a broad spectrum including:
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* Location information, which could come from a [[Global Positioning System|GPS]] receiver connected to the camera. [[As of 2004]] only a few cameras support this, though. Some people therefore use a normal receiver to track their movements, and then post-process the images by matching the timestamps in the images with the log from the receiver and can so add the missing information to images.
* Descriptions and copyright information. Again this is something which is most often done when post-processing the images, as only high-end camera models let the user choose a text for these fields. (Although this feature is becoming more and more apparent even in lower end compact [[digital cameras]]).
==Program support==
Exif data is embedded within the image file itself. While many recent [[Graphics software|image manipulation programs]] recognize Exif data and will maintain most of it when writing to a modified image, this is not the case for most older programs.
Many image gallery programs also recognise Exif data, and display it alongside the images.
==Problems==
The Exif standard has a number of drawbacks, mostly relating to its use of legacy file structure, including:
* The derivation of Exif from the [[Tagged Image File Format|TIFF]] file structure using offset pointers in the files means that data can be spread anywhere within a file, which means that software is likely to corrupt any pointers or corresponding data that it doesnt decode/encode. This is why most image editors damage or remove the Exif metadata to some extent upon saving.
* The tags available under the standard do not take into account modern digital cameras - Digital [[Single-lens reflex camera|SLR]]'s are very popular now, but the standard has no provision for adding metadata about the make, model or settings of lens, flash, filters or macro lenses fitted, nor dimensions of the sensor, details of the type of shutter or apeture,
* The standard only allows [[Tagged Image File Format|TIFF]] or [[JPEG]] files - there is no provision for a 'raw' file type which would be a direct data dump from the sensor device. This has caused camera manufacturers to invent many proprietory, incompatable 'raw' file formats.
* The JPEG and standard TIFF file formats supported by the standard are both limited to 24 bit colour. Many modern cameras can capture significantly more data than this but can only make use of it in a proprietory 'raw' format, hence the Exif standard helps reduce the motivation for camera manufacturers to provide higher colour-depth capabilities.
* Most digital cameras can also capture video - the Exif standard has no provision for video files.
* Exif is very often used in images created by scanners, however the standard makes no provisions for any scanner specific informationThe JPEG and standard TIFF file formats supported by the standard are both limited to 24 bit colour. Many modern cameras can capture significantly more data than this but can only make use of it in a proprietory 'raw' format, hence the Exif standard helps reduce the motivation for camera manufacturers to provide higher colour-depth capabilities.
* The standard defines a makernote tag, which allows camera manufacturers to place any custom format metadata in the file. This is increasingly used by camera manufacturers to store the myriad of camera setting types not listed in the Exif standard, such as shooting modes, post-processing settings, serial number, focusing modes. As the tag format is a manufacturer specific proprietory binary format, it can be impossible to retrieve information about these camera settings.
* Although there is no specified limit on the size of the embedded [[thumbnail]], it is not possible to have Exif metadata larger than 64kB in a [[JPEG]] image due to the restrictions of the [[JPEG]] file format. This has forced some camera manufacturers to create a non-standard way of placing a second (larger) thumbnail in the image for display on the camera's [[Liquid crystal display|LCD]]. Since it is a non standard extension, if a user re-saves the image using image editor software, then the second thumbnail will be lost, and the picture will no longer be compatable with the camera that took it.
==Capitalization==
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*[[Image processing]]
*[[DIG35]]
*[[Tag Image File Format / Electronic Photography|TIFF/EP]]
*[[eXtensible Metadata Platform|XMP]]
*[[Geocoded photo]]
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[[sv:Exif]]
[[zh:EXIF]]
===Makernote Information====
The 'Makernote' tag often contains interesting image information, however is normally in a proprietory binary format, however some formats have been able to be decoded:
*[http://ozhiker.com/electronics/pjmt/jpeg_info/makernotes.html Agfa, Canon, Casio, Epson, Fujifilm, Konica/Minolta, Kyocera/Contax, Nikon, Olympus, Panasonic, Pentax/Asahi, Ricoh, Sony ]
*[http://www.x3f.info/technotes/FileDocs/MakerNoteDoc.html Sigma/Foveon]
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