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Re: FlateDecode, ASCIIHexDecode, ASCII85Decode, and LZWDecode streams


From: Icarus Sparry
Subject: Re: FlateDecode, ASCIIHexDecode, ASCII85Decode, and LZWDecode streams
Date: Wed, 08 Dec 2010 15:16:11 -0000

On Sat, 26 Jun 2010 16:52:16 -0700, Fren Zeee wrote:

> On Jun 24, 12:53 am, bugbear <bugbear@trim_papermule.co.uk_trim> wrote:
>> Fren Zeee wrote:
>> > Dear All,
>>
>> > I have been playing for a while with files that have small bits of
>> > FlateDecode, ASCIIHexDecode, ASCII85Decode, and LZWDecode streams. My
>> > familiarity with these compression methods is limited to using the
>> > unix uncompress, gunzip and other compiled commands. At one time I
>> > was able to conveniently decode base64 fragments in emacs using the
>> > following commands.
>>
>> > base64-decode-region
>> >   Command: Base64-decode the region between BEG and END.
>>
>> > hexlify-buffer and dehexlify-buffer
>>
>> > Is there a solution within emacs or someone has a method to use
>> > libraries or to translate code from python/ruby etc. I could not find
>> > any (apropos decode) with reference to the above compression methods.
>>
>> > In ruby, FlateDecode and ASCII85Decode can be decompressed with
>> > existing ruby module which are zlib and Ascii85.
>>
>> The PostScript spec either directly, or via authoritative references,
>> documents the compression formats.
>>
>> Further, since PostScript (doh!) supports these formats, you can simply
>> use the Filter implementations in PostScript (e.g. GhostScript) to
>> decompress data.
>>
>>    BugBear
> 
> I did not get enough ideas so I am expanding my posting from
> 
> gnu.emacs.help, gnu.emacs.sources, gnu.emacs.gnus, comp.text.pdf
> 
> to
> 
> 
gnu.emacs.help,comp.lang.lisp,comp.compression,comp.lang.scheme,comp.text.pdf


Whilst one could write code to do this, you are better off using your 
existing knowledge and commands. In particular "shell-command-on-
region" (normal binding M-| ) allows you to feed a piece of a buffer 
through an external command such as the uncompress, and gunzip commands 
you list. If you invoke it with a prefix then the region is replaced by 
the output.




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