Sustainability of Digital Formats
 Planning for Library of Congress Collections

Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact
Format Description Categories >> Browse Alphabetical List

JPEG DCT Compression Encoding, Progressive

>> Back
Table of Contents
Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

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)
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_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

Local use Explanation of format description terms

LC experience or existing holdings See JPEG.
LC preference See JPEG.

Sustainability factors Explanation of format description terms

Disclosure Fully disclosed. Developed by the Joint Photographic Experts Group (JPEG), formally known as ISO/IEC JTC 1/SC 29/WG 10.
    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.

Quality and functionality factors Explanation of format description terms

Still Image
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.

File type signifiers Explanation of format description terms

Tag Value Note
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

Notes Explanation of format description terms

General  
History  

Format specifications Explanation of format description terms


Useful references

URLs


Last Updated: Tuesday, 12-Nov-2013 18:00:09 EST