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JPEG DCT Compression Encoding, Baseline

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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, baseline DCT sequential (formal name); Baseline JPEG (common name)
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_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

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 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.

Quality and functionality factors Explanation of format description terms

Still Image
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 tranforms (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.

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: 0xFFC0
Start of Frame (SOF) marker for baseline sequential DCT; see also JPEG

Notes Explanation of format description terms

General  
History  

Format specifications Explanation of format description terms


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Last Updated: Monday, 09-Dec-2013 16:40:20 EST