Exchangeable image file format is a standard that specifies the formats for images, sound,
and ancillary tags used by digital cameras, 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 for compressed image files, TIFF Rev. 6.0
for uncompressed image files, and RIFF WAV for audio files.
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.
Background The Japan Electronic Industries Development
Association produced the initial definition of Exif.
Version 2.1 of the specification is dated 12 June 1998.
JEITA established Exif version 2.2, dated 20 February 2002 and released in April 2002.
Version 2.21 is dated 11 July 2003, but was released in September 2003 following the release
of DCF 2.0.
The latest, version 2.3, released on 26 April 2010 and revised in May 2013, was jointly
formulated by JEITA and CIPA.
Exif is supported by almost all camera manufacturers.
The metadata tags defined in the Exif standard cover a broad spectrum:
Date and time information.
Digital cameras will record the current date and time and save this in the metadata.
Camera settings.
This includes static information such as the camera model and make, and information that
varies with each image such as orientation, aperture, shutter speed, focal length, metering
mode, and ISO speed information.
A thumbnail for previewing the picture on the camera's LCD screen, in file managers,
or in photo manipulation software.
Descriptions Copyright information.
Technical 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, which in effect holds an entire TIFF file within.
When Exif is employed in TIFF files, the TIFF Private Tag 0x8769 defines a sub-Image File
Directory 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, their
scope shall cover devices, recording media, and application software that handle them.
Geolocation
The Exif format has standard tags for location information.
As of 2014 many cameras and most 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.
Program support 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.
Problems Technical
The Exif format has a number of drawbacks, mostly relating to its use of legacy file
structures.
The derivation of Exif from the 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 doesn't decode/encode.
For this reason most image editors damage or remove the Exif metadata to some extent
upon saving.
The standard defines a MakerNote tag, which allows camera manufacturers to place any custom
format metadata in the file.
This is used increasingly by camera manufacturers to store myriad camera settings not listed
in the Exif standard, such as shooting modes, post-processing settings, serial number, focusing
modes, etc.
As this tag format is proprietary and manufacturer-specific, it can be prohibitively difficult to retrieve
this information from an image.
Some manufacturers encrypt portions of the information; for example, Nikon encrypts the
detailed lens data in their newer MakerNote data versions.
The standard only allows 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 proprietary, incompatible "raw" file
formats.
To solve this problem, Adobe developed the DNG format, in hopes that manufacturers would
standardize on a single, raw file format.
The Exif standard specifically states that color depth is always 24 bits.
However, many modern cameras, such as the Nikon D70 which captures 36 bits of color
per pixel, can capture significantly more.
Since Exif/DCF files cannot represent this color depth, many manufacturers have developed
proprietary, non-compatible Raw image formats.
Exif is very often used in images created by scanners, but the standard makes no provisions
for any scanner-specific information.
Photo manipulation software sometimes fails to update the embedded thumbnail after an
editing operation, possibly causing the user to inadvertently publish compromising information.
Exif metadata are restricted in size to 64 kB in JPEG images because according to the
specification this information must be contained within a single JPEG APP1 segment.
Although the FlashPix extensions allow information to span multiple JPEG APP2 segments, these
extensions are not commonly used.
This has prompted some camera manufacturers to develop non-standard techniques for storing
the large preview images used by some digital cameras for LCD review.
These non-standard extensions are commonly lost if a user re-saves the image using image
editor software, possibly rendering the image incompatible with the original camera that
created it.
There is no way to record time-zone information along with the time, thus rendering the stored
time ambiguous.
There is no field to record readouts of a camera's accelerometers or inertial navigation
system.
Such data could help to establish the relationship between the image sensor’s XYZ coordinate
system and the gravity vector.
It could also establish relative camera positions or orientations in a sequence of photos.
Privacy and security Since the Exif tag contains metadata 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.
Many users may be unaware that their photos are tagged by default in this manner, or that
specialist software may be required to remove the Exif tag before publishing.
For example, 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 therefore 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 a phone that had geotagged the image.
The photo's metadata included GPS coordinates locating McAfee in Guatemala, and he was captured
two days later.
According to documents leaked by Edward Snowden, the NSA is targeting Exif information under
the XKeyscore program.
Related standards Metadata Working Group was formed by a consortium
of companies in 2006 or 2007.
It released its first document on 24 September 2008, giving recommendations concerning the
use of Exif, IPTC and XMP metadata in images.
Extensible Metadata Platform was created by Adobe Systems to be a better metadata format
for photography and image processing.
However, it is generally unsupported in cameras.
Viewing and editing Exif data 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 that 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.
Example
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.
FlashPix extensions The Exif specification also includes a description
of FPXR 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: Exif audio files
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: MakerNote data
The 'MakerNote' tag contains image information normally in a proprietary binary format.
Some of these manufacturer-specific formats have been decoded:
OZHiker: Agfa, Canon, Casio, Epson, Fujifilm, Konica/Minolta, Kyocera/Contax, Nikon, Olympus,
Panasonic, Pentax/Asahi, Ricoh, Sony Kamisaka: Canon, Casio, FujiFilm, ISL, KDDI,
Konica/Minolta, Mamiya, Nikon, Panasonic, Pentax, Ricoh, Sigma, Sony, WWL
X3F Info: Sigma/Foveon ExifTool: Canon, Casio, FujiFilm, GE, HP,
JVC/Victor, Kodak, Leaf, Minolta/Konica-Minolta, Nikon, Olympus/Epson, Panasonic/Leica, Pentax/Asahi,
Reconyx, Ricoh, Samsung, Sanyo, Sigma/Foveon, Sony
Olypedia: Olympus 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.
See also Comparison of image viewers
Comparison of metadata editors Design rule for Camera File system
Digital photography eXtensible Metadata Platform
Geocoded photo Image file formats
IPTC Information Interchange Model Metadata Working Group
Tag Image File Format / Electronic Photography References
External links Exif standard version 2.3
Exif standard version 2.2 as PDF or as HTML Overview of the revisions to the DCF and Exif
standards Exif in the TIFF Tag Directory
Metadata working group List of Exif tags including MakerNote tags
The libexif C EXIF library Jeffrey's Exif Viewer