Sustainability of Digital Formats: Planning for Library of Congress Collections
Sustainability of Digital Formats: Planning for Library of Congress Collections |
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| Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact | |
| Full name | Exchangeable image file format for digital still cameras: Exif Version 2.2 |
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| Description |
Usually referred to as "TIFF file with Exif metadata." Exif specifications define files mainly intended for digital photography and TIFF_UNC_EXIF is one of two file types defined in the specification. Based on TIFF_6 (TIFF version 6, with extensions), TIFF_UNC_EXIF files can be read by many image software applications. Exif's special contribution is metadata beyond that typically provided in TIFF files. The Exif specification also provides a method for recording thumbnails and allows for the inclusion of audio in the WAVE format, to support such things as a photographer's 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 | |
| Subtype of | TIFF_UNC, TIFF, Uncompressed Bitmap |
| Affinity to | EXIF_2_2, Exif Exchangeable Image File Format. Version 2.2 specifies the metadata elements and syntax. |
| Affinity to | EXIF_Family, Exchangeable Image File Format (Exif) Family. Specification defines metadata elements for use in TIFF-EXIF. |
| LC experience or existing holdings | The Prints and Photographs Division and the Manuscript Division have collections containing digital-camera generated photographs in TIFF_UNC_EXIF. Specific Exif versions are unknown. |
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| LC preference | See the Library of Congress Recommended Formats Statement for format preferences for still image works. The RFS does not mandate or suggest the use of Exif data. |
| Disclosure | Fully disclosed; see TIFF_6 and EXIF_Family |
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| Documentation | See TIFF_6 and EXIF_Family |
| Adoption | Adoption level not known to the compilers of this document; JPEG_EXIF appears to be more widely adopted than TIFF_UNC_EXIF. |
| Licensing and patents | See TIFF_6 and EXIF_Family. |
| Transparency | See TIFF_UNC. |
| Self-documentation | Includes the tag sets or IFDs (Image File Directory) specified in both TIFF_6 and EXIF_Family. |
| External dependencies | None. |
| Technical protection considerations | None. |
| Still Image | |
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| Normal rendering | Good support. |
| Clarity (high image resolution) | Excellent. See also Notes. |
| Color maintenance | Excellent. The Exif tag set permits the identification of files that use sRGB.1 but does not include a 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 | Not applicable (stereo only). |
| Support for user-defined sounds, samples, and patches | Not applicable |
| Functionality beyond normal rendering | None. |
| Tag | Value | Note |
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| Filename extension | tif |
From EXIF version 2.2 standard. For comparison see TIFF_6 |
| Internet Media Type | image/tiff |
From IANA. Other MIME types may be in use. For comparison see TIFF_6 |
| Magic numbers | Hex: 49 20 49 ASCII: I<space>I |
For TIFF_6, from Gary Kessler's File Signatures. The compiler of this document does not know if TIFF_UNC_EXIF has different or additional magic numbers. |
| Pronom PUID | x-fmt/399 |
Exchangeable Image File Format (Uncompressed), Version 2.0. Exif Uncompressed Image (2.0). See http://www.nationalarchives.gov.uk/PRONOM/x-fmt/399. |
| Pronom PUID | x-fmt/388 |
Exchangeable Image File Format (Uncompressed), Version 2.1. Exif Uncompressed Image (2.1). See http://www.nationalarchives.gov.uk/PRONOM/x-fmt/388. |
| Pronom PUID | x-fmt/387 |
Exchangeable Image File Format (Uncompressed), Version 2.2. Exif Uncompressed Image (2.2). See http://www.nationalarchives.gov.uk/PRONOM/x-fmt/387. |
| Wikidata Title ID | See note. | Wikidata has no corresponding entry as of March 2023. |
| General |
From the specification:"Image data employs following existing image formats, depending on the image data type:
"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 applied similarly 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) 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 |
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| History | See EXIF_Family and EXIF_2_2. |
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.
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