[Coco] Radio Shack Catalogs Online Mirror

[Gene Heskett]

On Wednesday 24 December 2008, Torsten Dittel wrote:
>Gene Heskett schrieb:
>> That may be because the pdf's are in fact, one of the more powerfull
>> compressions that can be done.  Not even bzip2 can match it.
>
>Actually, Acrobat is optionally using ZIP for overall file compression.
>However, you can individually decide for any picture object the PDF
>contains, how it will be compressed. Assuming the catalog are one-page
>color scans only, you would select JPG compression when creating the
>file (1-Bit b&w scans might use TIFF compression instead, although my
>experiments showed, using ZIP in that case for picture object
>compressions is sometimes even the better choice).
>
>If you ZIP a JPEG file, it will become only a little bit smaller (but
>not much). If you ZIP  thae ZIPped JPEG again, it will get bigger (due
>to the overhead), because compressed data is not more compressible if
>the compression algorithm is good.
>
>Regards,
>Torsten
>
The PDF format is a true random access format, and spends considerable time 
looking for repeat phrases it can set up a 1 or 2 character 'dictionary' for.  
Properly done, this sort of setup can exceed bzip2 for compression ratio.  I 
have no idea if Adobe has patents on the method but bzip2 would probably 
invalidate them in court.  It is essentially bzip2 with a 64k dictionary.  
bzip2 rarely uses more than 12k, and it may even start a new dictionary if 
that one is used up.  Open a pdf file in an editor sometime, its very 
educational to follow what it is doing.
>
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-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
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