Sustainability of Digital Formats: Planning for Library of Congress Collections |
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Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact |
Full name | ISO/IEC 10918-3:1997. Information technology -- Digital compression and coding of continuous-tone still images, Extensions (formal name); JPEG extensions (common name) |
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Description |
A set of lossy compression encodings for full color and grayscale continuous-tone images that employ discrete cosine transforms (DCT) applied to 8-by-8-pixel Minimum Coded Unit (MCU) blocks, and that extend the capabilities beyond those provided by sequential baseline (JPEG_DCT_BL) and progressive (JPEG_DCT_PRG), and the several other encoding options offered in ISO/IEC 10918-1. The image-related extensions specified in ISO/IEC 10918-3 include (1) variable quantization within segments of an image, (2) selective refinement of portions of an image (hierarchical, progressive, and component), (3) tiling (simple tiling, pyramidal tiling [JTIP], composite tiling), and (4) the addition of a version number for compressed data formats and increasing the number of data units permitted in a minimum encoded unit. In addition, part 3 establishes the SPIFF file format. The JTIP subtype has been assigned PRONOM PUID fmt/149; the PRONOM Web page (consulted January 26, 2012) states that JTIP is a multi-resolution format, created for image presentation with easy transfer and handling, based on SPIFF. It allows presentation of images in various sizes and resolutions from vignette (1/16 screen size, used for browsing) through imagette (1/4 screen, for image comparison), to full screen and higher resolution images. Each layer is divided into tiles so the user can zoom or pan easily. . . ." |
Production phase | May be applied in initial-state picture creation; often used for middle- and final-state archiving or end-user delivery. |
Relationship to other formats | |
Subtype of | JPEG, JPEG Image Format Family |
Has subtype | JTIP, JPEG Tiled Image Pyramid Format, not described at this Web site at this time. |
Used by | JFIF_Family, JPEG File Interchange Format Family |
Used by | JFIF_1_02, JFIF JPEG File Interchange Format, Version 1.02 |
Used by | JFIF File Interchange Format, Versions 1.00 and 1.01, not described at this Web site at this time |
Used by | SPIFF, SPIFF Still Picture Interchange File Format |
Used by | JTIF File Format, a variant of TIFF, not described at this Web site at this time |
LC experience or existing holdings | See JPEG. |
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LC preference | See JPEG. |
Disclosure | Fully disclosed. Developed by the Joint Photographic Experts Group (JPEG), formally known as ISO/IEC JTC 1/SC 29/WG 10. |
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Documentation | ISO/IEC 10918-3:1997. Information technology -- Digital compression and coding of continuous-tone still images: Extensions. Also ISO/IEC 10918-3:1997/Amd 1:1999. Provisions to allow registration of new compression types and versions in the SPIFF header. Same as ITU-T Rec. T.84:1996, with Amd 1 1999. |
Adoption | The extent of adoption of JPEG extensions is not known to the compiler of this document. Comments welcome. |
Licensing and patents | See JPEG. |
Transparency | Depends upon algorithms and tools to read; will require sophistication to build tools. |
Self-documentation | See the file format descriptions for JFIF_1_02, SPIFF, and JPEG_EXIF. |
External dependencies | None. |
Technical protection considerations | None. |
Still Image | |
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Normal rendering | Good support. |
Clarity (high image resolution) | Good, but source data is limited to 8-bits-per-channel. Quality varies according to the sophistication of the encoding and the degree of compression applied. The extensions generally appear to affect how an image is segmented (e.g., tiling) or to allow for differential "refinement" of parts of an image, and do not seem to change the fundamentals of how encoding affects clarity, as compared to baseline JPEG images. Comments welcome. |
Color maintenance | See the file format descriptions for JFIF_1_02, SPIFF, and JPEG_EXIF. |
Support for vector graphics, including graphic effects and typography | No support for vector graphics. |
Support for multispectral bands | See JPEG. |
Functionality beyond normal rendering | Implied by the extensions themselves; not further investigated for this description. |
Tag | Value | Note |
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Filename extension | Not applicable. | See the file format descriptions for JFIF_1_02, SPIFF, and JPEG_EXIF. |
Internet Media Type | Not applicable. | See the file format descriptions for JFIF_1_02, SPIFF, and JPEG_EXIF. |
Magic numbers | Hex: 0xFF 0xD8 |
Start of Image (SOI) marker; see also JPEG |
Indicator for profile, level, version, etc. | See note. | Compiler of this description has not identified any Start of Frame (SOF) markers for part 3 extensions; Comments welcome. See also JPEG. |
General | |
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History |
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