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Hallo Aandi,

The strategy in this example is, that JPEG compressed streams contains
often large uniform byte sequences which can be compressed with Flate
compression.

In most cases, if a compressed JPEG stream contains such sequences, it
is a better idea to use directly Flate, LZW or CCITT compression,
because the image contains often large uniform coloured surfaces.

However, may be that is the best strategy for these images...

Greetings

Jens Boschulte
www.dynaforms.com



-----Urspr�ngliche Nachricht-----
Von: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] Im Auftrag von Aandi Inston
Gesendet: Donnerstag, 4. Dezember 2003 10:47
An: [EMAIL PROTECTED]
Betreff: [PDFdev] Applying FlateDecode to a DCTDecode stream

I have now seen several examples of PDF files (made, I think,
by InDesign or by Mac OS X but I can't confirm), which have 
streams compressed first with DCTDecode (JPEG) then with 
FlateDecode (ZIP).  

Although this is clearly legal in PDF terms, it also seems 
pointless or counterproductive.  Fortunately it doesn't seem
to upset any of my code, but having compression reported
as ZIP, JPEG does startle both me and our users!  

Does anyone have any ideas or background on why we are seeing
this bizarre compression strategy?

Aandi Inston
Quite Software


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