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|Developed by||JEITA, CIPA|
|Latest release||2.3 / 26 April 2010|
|Extended from||TIFF, JPEG, WAV|
|Developed by||JEITA, CIPA|
|Latest release||2.3 / 26 April 2010|
|Extended from||TIFF, JPEG, WAV|
Exchangeable image file format (Exif) is a standard that specifies the formats for images, sound, and ancillary tags used by digital cameras (including smartphones), scanners and other systems handling image and sound files recorded by digital cameras. The specification uses the following existing file formats with the addition of specific metadata tags: JPEG Discrete cosine transform (DCT) for compressed image files, TIFF Rev. 6.0 (RGB or YCbCr) for uncompressed image files, and RIFF WAV for audio files (Linear PCM or ITU-T G.711 μ-Law PCM for uncompressed audio data, and IMA-ADPCM for compressed audio data). It is not supported in JPEG 2000, PNG, or GIF.
This standard consists of the Exif image file specification and the Exif audio file specification.
The Japan Electronic Industries Development Association (JEIDA) produced the initial definition of Exif. Version 2.1 of the specification is dated June 12, 1998. JEITA established version 2.2 in April 2002. The latest, version 2.3 dated April 2010, was jointly formulated by JEITA and CIPA. Though the specification is not currently maintained by any industry or standards organization, almost all camera manufacturers use it.
The metadata tags defined in the Exif standard cover a broad spectrum:
The Exif tag structure is borrowed from TIFF files. On several image specific properties, there is a large overlap between the tags defined in the TIFF, Exif, TIFF/EP, and DCF standards. For descriptive metadata, there is an overlap between Exif and IPTC Information Interchange Model info, which also can be embedded in a JPEG file.
When Exif is employed for JPEG files, the Exif data are stored in one of JPEG's defined utility Application Segments, the APP1 (segment marker 0xFFE1), which in effect holds an entire TIFF file within. When Exif is employed in TIFF files (also when used as "an embedded TIFF file" mentioned earlier), the TIFF Private Tag 0x8769 defines a sub-Image File Directory (IFD) that holds the Exif specified TIFF Tags. In addition, Exif also defines a Global Positioning System sub-IFD using the TIFF Private Tag 0x8825, holding location information, and an "Interoperability IFD" specified within the Exif sub-IFD, using the Exif tag 0xA005.
Formats specified in Exif standard are defined as folder structures that are based on Exif-JPEG and recording formats for memory. When these formats are used as Exif/DCF files together with the DCF specification (for better interoperability among devices of different types), their scope shall cover devices, recording media, and application software that handle them.
The Exif format has standard tags for location information. As of 2012[update] a few cameras and a growing number of mobile phones have a built-in GPS receiver that stores the location information in the Exif header when a picture is taken. Some other cameras have a separate GPS receiver that fits into the flash connector or hot shoe. Recorded GPS data can also be added to any digital photograph on a computer, either by correlating the time stamps of the photographs with a GPS record from a hand-held GPS receiver or manually by using a map or mapping software. The process of adding geographic information to a photograph is known as geotagging. Photo-sharing communities like Panoramio, locr or Flickr equally allow their users to upload geocoded pictures or to add geolocation information online.
Most of Nokia's Nseries mobile phones (such as the N95) have a GPS receiver and use Location Tagger, a piece of software from Nokia Beta Labs. All captured images are tagged with corresponding GPS coordinates when a GPS signal is available. The second generation of iPhone (known as the iPhone 3G) by Apple Inc. is also equipped with a GPS receiver and uses the receiver to geotag photographs taken with the device. Subsequent generations (the iPhone 3GS, 4 & 4S) also support this feature. The first generation iPhone is not equipped with GPS, and uses a service provided by Skyhook to triangulate and approximate the location at which a picture was taken - using nearby cellular-phone towers and WiFi hot-spot signal-strength data. The Skyhook service provides approximate GPS location information which is then added to the Exif data associated with the picture. Also mobile phones with the Android operating system as well as BlackBerry smartphones with a camera and built-in GPS or Bluetooth GPS add-ons can geotag images with the included camera application.
Exif data are embedded within the image file itself. While many recent image manipulation programs recognize and preserve Exif data when writing to a modified image, this is not the case for most older programs. Many image gallery programs also recognise Exif data and optionally display it alongside the images.
Software libraries, such as libexif for C and Adobe XMP Toolkit or Exiv2 for C++, Metadata Extractor for Java, or Image::ExifTool for Perl, parse Exif data from files and read/write Exif tag values.
Apart from not being a maintained standard, the Exif format has a number of drawbacks, mostly relating to its use of legacy file structures.
Since the Exif tag contains information about the photo, it can pose a privacy issue. For example, a photo taken with a GPS-enabled camera can reveal the exact location and time it was taken, and the unique ID number of the device - this is all done by default - often without the user's knowledge. By removing the Exif tag with software such as ExifTool before publishing, the photographer can avoid possible problems. Many users may be unaware that their photos are tagged in this manner. A whistleblower, journalist or political dissident relying on the protection of anonymity to allow them to report malfeasance by a corporate entity, criminal, or government may find their safety compromised by this default data collection.
In December 2012, anti-virus programmer John McAfee was arrested in Guatemala while fleeing from alleged persecution in Belize, which shares a border. Vice magazine had published an exclusive interview with McAfee "on the run" that included a photo of McAfee with a Vice reporter taken with an iPhone 4S smart phone. The photo's metadata included GPS coordinates locating McAfee in Guatemala, and he was captured two days later.
Metadata Working Group was formed by a consortium of companies in 2006 (according to their web page) or 2007 (as stated in their own press release). It released its first document on 24 September 2008, giving recommendations concerning the use of Exif, IPTC and XMP metadata in images.
In Windows XP, a subset of the Exif information may be viewed by right clicking on an image file and clicking properties; from the properties dialog click the Summary tab and then the Advanced button. However, using this tab to edit Exif information may damage certain Exif headers. As of the release of Service Pack 3, Windows XP still shows evidence of corrupting Exif tags when modifying JPG file properties via the file properties window.
On Mac OS X 10.4 and above, basic Exif information may be viewed in the Finder by doing Get Info on a file and expanding the More Info section.
On Unix systems using the GNOME desktop environment, a subset of Exif data can be seen by right clicking the file in the Nautilus file manager and selecting properties. In KDE, it can be seen by right clicking in the Dolphin file manager, selecting "Properties" and then "Information". Many Unix image viewers give the full set of Exif data.
In addition, there are many software tools available which allow both viewing and editing of Exif data.
Sharing photographs with Exif information may present privacy problems such as revealing a location. Such information may be edited out before sharing the file. Alternatively, there are metadata removal tools that will remove Exif information.
The following table shows Exif data for a photo made with a typical digital camera. Notice that authorship and copyright information is generally not provided in the camera's output, so it must be filled in during later stages of processing. Some programs, such as Canon's Digital Photo Professional, allow the name of the owner to be added to the camera itself.
|Orientation (rotation)||top - left [8 possible values]|
|Date and Time||2003:08:11 16:45:32|
|Exposure Time||1/659 sec.|
|Exif Version||Exif Version 2.1|
|Date and Time (original)||2003:08:11 16:45:32|
|Date and Time (digitized)||2003:08:11 16:45:32|
|ComponentsConfiguration||Y Cb Cr -|
|Compressed Bits per Pixel||4.01|
|Flash||Flash did not fire.|
|Focal Length||20.1 mm|
|MakerNote||432 bytes unknown data|
|FlashPixVersion||FlashPix Version 1.0|
The Exif specification also includes a description of FPXR (FlashPix-Ready) information which may be stored in APP2 of JPEG images using a structure similar to that of a FlashPix file. These FlashPix extensions allow meta information to be preserved when converting between FPXR JPEG images and FlashPix images. FPXR information may be found in images from some models of digital cameras by Kodak and Hewlett-Packard. Below is an example of the FPXR information found in a JPEG image from a Kodak EasyShare V570 digital camera:
|Used Extension Numbers||1|
|Extension Name||Screen nail|
|Extension Class ID||10000230-6FC0-11D0-BD01-00609719A180|
|Extension Persistence||Invalidated By Modification|
|Extension Create Date||2003:03:29 17:47:50|
|Extension Modify Date||2003:03:29 17:47:50|
|Extension Description||Presized image for LCD display|
|Storage-Stream Pathname||/.Screen Nail_bd0100609719a180|
|Screen Nail||(124498 bytes of data containing 640x480 JPEG preview image)|
The Exif specification describes the RIFF file format used for WAV audio files, and defines a number of tags for storing meta information such as artist, copyright, creation date, and more in these files. The following table gives an example of Exif information found in a WAV file written by the Pentax Optio WP digital camera:
|Avg Bytes Per Sec||7872|
|Bits Per Sample||8|
|Related Image File||IMGP1149.JPG|
|Model||PENTAX Optio WP|
|MakerNote||(2064 bytes of data)|
The 'MakerNote' tag contains image information normally in a proprietary binary format. Some of these manufacturer-specific formats have been decoded:
Unfortunately, the proprietary formats used by many manufacturers break if the MakerNote tag is moved - i.e. by inserting or editing a tag which precedes it. The reason to edit to the Exif data could be as simple as to add copyright information, an Exif comment, etc. In some cases, camera vendors also store important information only in proprietary makernote fields, instead of using available Exif standard tags. An example for this is Nikon's ISO settings tag.
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