LZW compression

[Alejandro Tejada]

on Sat, 3 Jan 2004
Alex Rice wrote:

> I thought the gzip compress() was Rev's only
> compression feature?

Look at this page:

<http://www-vis.lbl.gov/software_support/ghostview/docs/Language.htm#Standard_filters>

"the data compression method variously known
as 'zlib' (the name of a popular library that
implements it), 'Deflate' (as in RFC 1951, which 
is a detailed specification for the method), 
'gzip' (the name of a popular compression application
that uses it), or 'Flate' (Adobe's name).

and this:

<http://mail.python.org/pipermail/python-dev/1999-December/001617.html>

I spent a long time figuring out what Adobe 
PDF's "flate filter" was before I discovered
it was the inverse of "deflate" (yes, there were 
loud sounds of head-slapping when I clicked) and 
discovered that zlib.compress() was EXACTLY what
you need to create compressed streams in 
PDF documents.


> re: base64Encode it converts the data to all ASCII
> suitable for MIME attachements. The size is 
> much larger than the source data.

I was wrong on this. MD5digest and PNG are the other
filters that could be used in pdf documents.

al

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