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JPEG DCT Compression Encoding, Extensions

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name ISO/IEC 10918-3:1997. Information technology -- Digital compression and coding of continuous-tone still images, Extensions (formal name); JPEG extensions (common name)
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_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 10918-3:1997. 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.

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. 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.

File type signifiers Explanation of format description terms

Tag Value Note
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.

Notes Explanation of format description terms

General  
History  

Format specifications Explanation of format description terms


Useful references

URLs


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