Computer World. Матросова Т.А. - 102 стр.

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times that amount. Use of digital images often is not viable due to high storage or
transmission costs, even when image capture and display devices are quite affordable.
Modern image compression technology offers a possible solution. State-of-the-
art techniques can compress typical images from 1/10 to 1/50 their uncompressed
size without visibly affecting image quality. But compression technology alone is not
sufficient. For digital image applications involving storage or transmission to become
widespread in today's marketplace, a standard image compression method is needed
to enable interoperability of equipment from different manufacturers.
For the past few years, a standardization effort known by the acronym JPEG, for
Joint Photographic Experts Group, has been working toward establishing the first
international digital image compression standard for continuous-tone (multilevel) still
images, both grayscale and color.
Photovideotex, desktop publishing, graphic arts, color facsimile, newspaper
wirephoto transmission, medical imaging, and many other continuous-tone image
applications require a compression standard in order to develop significantly beyond
their present state. JPEG has undertaken the ambitious task of developing a general-
purpose compression standard to meet the needs of almost all continuous-tone still-
image applications.
If this goal proves attainable, not only will individual applications flourish, but
exchange of images across application boundaries will be facilitated. This latter
feature w ill bec ome inc reasingly important as more image applic ations are
implemented on general-purpose computing systems, which are themselves becoming
increasingly interoperable and internetworked. For applications which require
specialized VLSI to meet their compression and decompression speed requirements, a
common method will provide economies of scale not possible within a single
application.
This article gives an overview of JPEG's proposed image-compression standard.
Readers without prior knowledge of JPEG or compression based on the Discrete
Cosine Transform (DCT) are encouraged to study first the detailed description of the
Baseline sequential codec, which is the basis for all of the DCT-based decoders.
While this article provides many details, many more are necessarily omitted.
Some of the earliest industry attention to the JPEG proposal has been focused on
the Baseline sequential codec as a motion image compression method – of the
«intraframe» class, where each frame is encoded as a separate image.
Background: Requirements and Selection Process
JPEG's goal has been to develop a method for continuous-tone image
compression which meets the following requirements :
1) be at or near the state of the art with regard to compression rate and
accompanying image fidelity, over a wide range of image quality ratings, and
especially in the range where visual fidelity to parameterizable, so that the
application (or user) can set the desired compression/quality tradeoff;
2) be applicable to practically any kind of continuous-tone digital source
image (i.e. for most practical purposes not be restricted to images of certain

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