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JBIG2 Compression
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. |
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