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Exif Exchangeable Image File Format, Version 2.2

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name Exchangeable image file format for digital still cameras: Exif, Version 2.2
Description

The Exif specifications define a pair of file types, mainly intended for recording technical details associated with digital photography. The two types employ different image encodings based on existing image formats and the resulting files can be read by many image software applications. The Exif metadata shared by the two file types represents an extension to each of the underlying types.

Uncompressed files are recorded in TIFF Rev. 6.0 (TIFF_6) format, with an extended set of tags; see Tags for TIFF and Related Specifications. Compressed Exif files are recorded as baseline JPEG (ISO/IEC 10918-1) with metadata-containing application marker segments (APP1 and APP2) inserted.

The extended metadata defined by Exif is subsumed within the TIFF/EP specification; thus TIFF/EP can be seen as a successor-replacement to TIFF_UNC_EXIF.

Exif 2.2, also termed Exif Print, introduced tags to record camera settings, including scene type (portrait, landscape, night scene, etc.), that can be used to guide automatic adjustments before printing in order to best match the photographer's intent. The key difference between Exif 2.21 and Exif 2.2 is support for the Adobe RGB color space without embedding a color profile. In version Exif 2.2, the default color space is sRGB.

The Exif specification also provides a method for recording thumbnails and allows for the inclusion of audio in the WAVE format, to support such elements as photographers' spoken annotations.

Production phase Generally applied by cameras in initial-state picture creation; may also be used for middle- and final-state archiving or end-user delivery.
Relationship to other formats
    Has earlier version Exif Versions 2.0 and 2.1, not documented here
    Has later version Exif Version 2.3, not documented here at this time.
    Affinity to JPEG_EXIF, JPEG encoded file with Exif metadata. Specified in same standard.
    Affinity to TIFF_UNC_EXIF, TIFF uncompressed file with Exif metadata. Specified in same standard.

Local use Explanation of format description terms

LC experience or existing holdings Prints and Photographs Division holds a modest number of digital-camera generated photographs in JPEG_EXIF.
LC preference General preference for bitmapped still images is for uncompressed; rich metadata always welcome. Thus, for digital-camera photographs, TIFF_UNC_EXIF would be preferred (TIFF_UNC acceptable); JPEG_EXIF is acceptable and preferred to JFIF (also acceptable).

Sustainability factors Explanation of format description terms

Disclosure Fully documented; developed under the auspices of JEITA (Japan Electronics and Information Technology Industries Association). Since 2009, JEITA and CIPA (Camera and Imaging Products Association) have jointly managed the Exif standard.
    Documentation JEITA CP-3451; Exchangeable image file format for digital still cameras: Exif Version 2.2, April 2002.
Adoption Supported by almost all digital cameras. See TIFF_UNC_EXIF and JPEG_EXIF.
    Licensing and patents None
Transparency Depends upon encoding; see TIFF_UNC_EXIF and JPEG_EXIF.
Self-documentation See TIFF_UNC_EXIF and JPEG_EXIF. Exif tags are included in Tags for TIFF and Related Specifications.
External dependencies None
Technical protection considerations None

Quality and functionality factors Explanation of format description terms

Still Image
Normal rendering Good support.
Clarity (high image resolution) See TIFF_UNC_EXIF and JPEG_EXIF. See also Notes.
Color maintenance See TIFF_UNC_EXIF and JPEG_EXIF. The Exif 2.2 tags permits the identification of files that use sRGB.1 Exif 2.21 also allows identification of the Adobe RGB color profile. There appears to be no Exif tag for the ICC profile2 for a capture device. See also Notes.
Support for vector graphics, including graphic effects and typography No support for vector graphics.
Functionality beyond normal rendering Supports thumbnails and audio content.
Sound
Normal rendering Good support.
Fidelity (high audio resolution) Good, depending on encoding, sampling frequency, and word length. Exif supports the following encodings: LPCM and μ-Law PCM (conforming to ITU-T G.711) for uncompressed audio data; IMA ADPCM (Adaptive Differential PCM) for compressed audio data. Highest fidelity from LPCM is limited in this standard to CD quality (44.1 kHz sampling and 16 bit words).
Multiple channels Stereo only.
Support for user-defined sounds, samples, and patches None
Functionality beyond normal rendering None.

File type signifiers Explanation of format description terms

Tag Value Note
Filename extension See related format. 

See TIFF and JPEG_EXIF

Internet Media Type See related format. 

See TIFF and JPEG_EXIF

Magic numbers See related format. 

See TIFF and JPEG_EXIF


Notes Explanation of format description terms

General

From the specification:"Image data employs following existing image formats, depending on the image data type:

  • RGB uncompressed data: Baseline TIFF Rev. 6.0 RGB Full Color Images,
  • YCbCr uncompressed data: TIFF Rev. 6.0 Extensions YCbCr Images,
  • JPEG compressed data: JPEG Baseline ADCT." (page 8)

"The combination of pixel composition and pixel sampling for image data shall be RGB 4:4:4 and either Y:Cb:Cr =4:2:2 or Y:Cb:Cr = 4:2:0. The pixel composition of image data shall also be 8 bits each. This specification is appliedsimilarly to thumbnails. As sampling points on the elements making up pixels, the Y and Cb,Cr sampling points may be either co-sited or centered. . . . In the case of Y:Cb:Cr = 4:2:2, spatial co-siting is recommended for the sake of improved image quality on TV systems. For Y:Cb:Cr = 4:2:0, spatial centering is recommended as per the TIFF default and is most common format of the personal computer applications." (page 5)

History

Timeline for Exif development:

  • Version 1.0. Published October 1995.
  • Version 1.1. Published May 1997
  • Version 2.0. Published November 1997.
  • Version 2.1. Published December 1998.
  • Version 2.2. Published April 2002.
  • Version 2.21. Published September 2003 as a set of changes. Promoted as "Exif Print."
  • Unified Version 2.21. Published September 2009.
  • Version 2.3. Published April 2010.
  • Version 2.3 (Revised 2012). Published December 2012 (with two explanations corrected).

About JEITA: "The Japan Electronics and Information Technology Industries Association (JEITA) was formed on November 1, 2000, through the merger of the Electronic Industries Association of Japan (EIAJ) and Japan Electronic Industries Development Association (JEIDA). JEITA is a new industry organization in Japan with activities covering both the electronics and information technology (IT) fields." (http://www.jeita.or.jp/english/about/what/).

About CIPA: The Camera and Imaging Products Association (CIPA) was established in 2002 as a successor organization to the Japan Camera Industry Association (JCIA). JCIA participated in the original development of Exif. CIPA "is an industry association consisting of companies engaged in the development, production, or distribution of digital cameras, imaging-related products, and software" (http://www.cipa.jp/guide/documents/e/en0203.pdf).


Format specifications Explanation of format description terms


Useful references

URLs

1The color space sRGB, standardized as IEC 61966-2-1, establishes an image viewing environment with a known color temperature (6500 degrees Kelvin) and gamma (2.2), thus increasing the user's ability to maintain color.

2The most effective color maintenance systems rely on the existence of an ICC (International Color Consortium) profile of the capture device, which can then be compared to profiles for output devices, permitting appropriate adjustments of image color. The TIFF tag for the ICC profile (tag 34675, InterColourProfile) has been added as a "private" extension in the TIFF/IT and TIFF/EP standards. Extended tags of this kind may be used in any TIFF_6 file, although they may not be recognized by all readers.


Last Updated: 02/27/2014