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 | ISO/IEC 10918-1:1994. Information technology -- Digital compression and coding of continuous-tone still images, progressive DCT-based (formal name); Progressive 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, and encodes similar-positioned coefficients of all 8-by-8-pixel Minimum Coded Unit (MCU) blocks in one action, followed by the next positioned coefficients of all blocks, etc. When a progressive image is decoded, "every other line" appears, displaying a top-to-bottom image relatively quickly; following this, the missing lines are filled in. The encoding and related matters are well described in the ISO specification and on Web sites like those cited in Useful references in this description. |
| 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, 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 10918-1:1994, Information technology -- Digital compression and coding of continuous-tone still images: Requirements and guidelines. Same as ITU-T Rec. T.81:1992. |
| Adoption | 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, considering that the 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 tranforms (DCT) produce less clarity than discrete wavelet tranforms (DWT), used by J2K (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: 0xFFC2 |
Start of Frame (SOF) marker for progressive DCT; see also JPEG |
| General | |
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| History |
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