Document imaging applications are often a trade-off between quality and compression.  As technology has improved, and colour become the norm for many publication formats, so user quality expectations have also increased.  As there is often a requirement for accurate on-screen viewing, as well as the ability to print high quality facsimiles of an original document, compression requirements are often conflicting.  Many documents contain areas which are best communicated in character coded text format (to allow for optimum compression and indexing), together with photographic or half-toned images, graphics and other image types.

There is a need for hybrid coding schemes in which each type of text on a page can be compressed optimally using a wide variety of coding schemes. ITU-T have defined (in their Recommendation T.44) 'Mixed Raster Coding' in which a page can be split into different regions, each with its own compression type.  Because of the close liaison between the JPEG and JBIG committees and ITU-T, original JPEG (IS 10918-1), JPEG-LS (IS 14495-1) and JPEG 2000 (IS 15444), as well as JBIG (IS 11544) and JBIG2 (IS 14492) can all be used as valid compression types, as well as existing fax and other formats.

One specific development within the JPEG 2000 set of standards is the 'JPM' Compound Image File Format defined in Part 6 of the JPEG 2000 standard.  This extension to the basic JPEG 2000 file format (defined in parts 1 and 2 of the Standard) adds in the concepts and syntax necessary to handle compound documents coded in MRC format. 

The resulting standard shows how a wide variety of different techniques can be applied to make very real savings (up to an order of magnitude better than just one compression scheme by itself) for document imaging systems. 

For more information contact:

Rob Buckley, Xerox Corporation
or
Lou Sharpe, Picture Elements Inc