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 10918-1:1994. Information technology -- Digital compression and coding of continuous-tone still images, baseline DCT sequential (formal name); Baseline JPEG (common name) |
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Description |
Lossy compression encoding for full color and grayscale continuous-tone images that employs discrete cosine transforms (DCT) and other processes. In baseline encoding, the 8-by-8 pixel Minimum Coded Unit (MCU) blocks that comprise the image are input sequentially; the coefficients of a single block are encoded in a zigzag manner. When decoded, the image appears from top to bottom like a windowshade rolling down. Compression is variable and governed by a number of parameters; typical settings provide from 10:1 to 20:1 reductions in file size. See also JPEG. JPEG_DCT_BL has been assigned PRONOM PUID: x-cmp/11. |
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 Encoding Family |
Used by | JFIF_Family, JPEG File Interchange Format Family |
Used by | JFIF_1_02, 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, Still Picture Interchange File Format |
Used by | JPEG_EXIF, JPEG Encoded File with Exif Metadata |
Used by | JTIF File Format, a variant of TIFF, not described at this Web site at this time |
Used by | DNG_1_6, Adobe Digital Negative (DNG), Version 1.6 |
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 10918-1:1994. Information technology -- Digital compression and coding of continuous-tone still images: Requirements and guidelines. Same as ITU-T Rec. T.81:1992. |
Adoption | Very widely adopted. |
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. Most commentators agree that, at the same compression ratios, discrete cosine transforms (DCT) produce less clarity than discrete wavelet tranforms (DWT), used by J2K_C (JPEG 2000) and other compression algorithms. |
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 | Not investigated for this format description. |
Tag | Value | Note |
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Filename extension | Not applicable. | See JFIF_1_02, SPIFF, and JPEG_EXIF. |
Internet Media Type | Not applicable. | See 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. | Hex: 0xFFC0 |
Start of Frame (SOF) marker for baseline sequential DCT; see also JPEG |
General | |
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History |
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