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Subject: [Tiff] Re: JBIG2 in TIFF
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tiff-request@lists.maptools.org wrote:

>Message: 1
>Date: Sun, 13 May 2007 10:47:29 -0700 (PDT)
>From: t t <questionwood@yahoo.com>
>Subject: [Tiff] JBIG2 compressed TIF question about bpp
>To: tiff@lists.maptools.org
>
>Hi everybody,
>
>I've used this site many times before to look up TIFF tags and look at the TIFF specification.  My question is about a JBIG2-compressed TIF.  Now I know JBIG2 is a bitonal compression standard, but if you save let's say a 24-bit TIF with JBIG2 compression should it work according to the specification or do you have to start with a 1-bit TIF first?
>
>I'm using some imaging software and I can successfully start with a 24-bit TIF and save it as a PDF with JBIG2 compression so it's 1 bit.  But if I start with a 24-bit TIF and save it as a TIF with JBIG2 compression an exception is thrown, but if start with a 1-bit TIF and save it as a TIF with JBIG2 compression it works fine as it should.  I know if you start with a non 1-bit TIF and save it with G4 compression it will take it to 1-bit without a problem.
>  
>
JBIG2 compression in TIFF was only recently added as an extension to the 
TIFF/IT spec via an ISO addendum to TIFF/IT.   As far as I'm aware, no 
attempt has been made yet to support it in tifflib (if anyone is 
thinking about this, I'd like to talk to them, as I'm interested in 
supporting it in SwiftView - just as we already support JBIG2 in PDF.)

As with any other bitonal compression standard, non-bitonal images must 
be converted to bitonal before you can compress with JBIG2.

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