Sustainability of Digital Formats
Planning for Library of Congress Collections
Sustainability of Digital Formats
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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 (formal name) TIFF_UNC_EXIF is one of two file types defined. TIFF file with Exif metadata (common name) |
| Description | 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. |
| LC experience or existing holdings | None. |
| 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 and TIFF_UNC very acceptable; JPEG_DCF and JPEG_EXIF are acceptable and preferred to JFIF (also acceptable). Emerging formats under consideration include two variants of JPEG 2000: J2K_LL (core lossless) and J2K_LSY (core lossy). |
| Disclosure | Fully disclosed; see TIFF_6 and EXIF_2_2. |
| Documentation | See TIFF_6 and EXIF_2_2. |
| Adoption | Adoption not known to the compilers of this document; JPEG_EXIF appears to be more widely adopted than TIFF_UNC_EXIF. |
| Licensing and patent claims | See TIFF_6 and EXIF_2_2. |
| Transparency | See TIFF_UNC. |
| Self-documentation | Includes the tag sets or IFDs (Image File Directory) specified in both TIFF_6 and EXIF_2_2. |
| External dependencies | None. |
| Technical protection considerations | None. |
| Still images | |
| Normal rendering for still images | Good support. |
| Clarity (support for 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 graphic effects and typography | No support for vector graphics. |
| Functionality beyond normal image rendering | Supports thumbnails and audio content. |
| Sound | |
| Normal rendering for sound | Good support. |
| Fidelity (support for 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). |
| Support for multiple sound channels | Not applicable (stereo only). |
| Support for downloadable or user-defined sounds, samples, and patches | Not applicable |
| Functionality beyond normal rendering for sound | None. |
| Tag type | Value | Note |
| Filename Extension | tif | May be additional types; for comparison see TIFF_6 |
| Internet Media Type | image/tiff | May be additional types; for comparison see TIFF_6 |
| Magic numbers |
[Hex: 49 49 ASCII: II] [See next cell] | For TIFF_6, from from Gary Kessler's File Signatures. The compiler of this document does not know if TIFF_UNC_EXIF has different or additional magic numbers. |
| 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 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 |
| History | See EXIF_2_2. |
URLs
• http://partners.adobe.com/asn/developer/PDFS/TN/TIFF6.pdf
• http://www.exif.org/specifications.html
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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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