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Date: Wed, 30 Apr 2003 10:04:04 -0400
From: Tom Kacvinsky <tjk@ams.org>
To: tiff@olympiakos.com
Subject: tiff2ps and /DCTDecode filter
Message-ID: <2147483647.1051697044@tjk.ams.org>
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Hi all,

I am trying to get the /DCTDecode filter for JPEG compressed TIFF images to
work.

What I have found is that neither the Quantization tables nor the Huffman
tables make it into the strip/tile data, so any Adobe DCTDecode filter will
choke with a message like:

%%[ Error: ioerror; OffendingCommand: image; ErrorInfo: DCTDecodeFilter JPEG
SOFn DQT or DHT marker missing before SOS marker ]%%

But, there is a JPEGTables entry in the TIFF image.  My thought on this
is to use this data to get the Huffman tables or Quantization tables and
then make the appropriate filter dictionary:

  <<
    /Colors 3
	/QuantTables [ ... ]
	/HuffTables [ ... ]
  >> /DCTDecode filter

Where can I find documentation on the JPEGTables entry?  In the TIFF v6.0 spec?

There are also going to be issues with SamplesPerPixel and he Photometric
interpretation.  I am still learning about this stuff, so it will be a while
before I get my head wrapped around it.

The issues I see with this are (a) I am not sure if the Adode DCTDecode filter
will use the information passed in the filter dictionary in lieu of the SOFn
JPEG markers and (b) what about different strips/tiles having different quant
and/or huff tables?

Thoughts?  Tom Lane, if you are still on the libtiff mailing list, I would
really
appreciate your thoughts on this.  I know there are "issues" with using the IJG
JPEG library to make JPEG streams that Adobe's interpreters grok...


Regards,

Tom

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