JBIG2 how do I love thee, let me count the ways. Why do I love JBIG2 so much?
Well lets start out by backtracking a little. After 23 years in the
imaging business I have seen a number of new file formats and compression algorithms.
Remember FlashPix? (just thought I'd throw that in for laughs)
They are announced with all kinds of incredible claims like100 times
better than JPEG or Group 4. Whether true or not (rarely true), they are
in most cases a proprietary file format owned by one company. Therefore
viewers are hard to find and wide spread adoption is rare. Also if the one
single source goes out of business you have no way of converting the images you
are left with.
Enter JBIG2. JBIG2 an ISO standard T.84 and a specification is
publicly available. So what, you say. Here's the best part. JBIG2
is supported by PDF as a compression filter. This means you can create a JBIG2
compressed PDF file and any one with Adobe Acrobat 5.0 or greater can view the
image. So most desktops already have a JBIG2 viewer installed.
Oh yeah by the way it does compress well. I have found JBIG2 to
compress 7 times better than Group 4 compression. An image uncompressed 1
meg was compressed in Tiff group 4 to 82k. JBIG2 was able to compress
down to 12k.
If you must know JBIG2 creates a symbol table. Usually text characters in the image. After the table is built redundant symbols can be eliminated. This can be done be creating a tolerance for lossy compression or exact for lossless compression.
-Jim
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