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Date: Tue, 20 Sep 1994 09:53:50 +0200
From: Fredrik Lundh <fredrik@kalle.teragon.ivab.se>
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To: davisonj@ecn.purdue.edu
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In-Reply-To: <MAILQUEUE-102.940920055650.384@delkp1.doceye.ivab.se> (message from John M Davison on Mon, 19 Sep 1994 22:03:48 -0500 (EST))
Subject: Re: TIFF CIEL*a*b* Question (with Answer)
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> It would seem, then, that Compression values of 2 (CCITT Group 3
> 1-Dimensional Modified Huffman run-length encoding), 3
> (T4-encoding), and 4 (T6-encoding) are acceptable only for images in
> which all of the following conditions are satisfied:
>          o  BitsPerSample[0] is equal to 1.
>          o  PhotometricInterpretation is 0 or 1.
>          o  m = (number of ExtraSamples) is equal to SamplesPerPixel
>             minus 1.

You could use m > 1 and PlanarConfiguration=2, and why not
PhotometricInterpretation=3.

But don't ship such files outside your office...  When using
Compression=3 or 4, I'd stick to SamplesPerPixel=1,
PhotometricInterpretation=0, and RowsPerStrip=ImageLength!

I believe things like the CCITT encodings (especially T4/T6), JPEG,
and (even) colour separations are _accommodated_ by the TIFF-spec, not
defined by it. The idea of putting them into the TIFF-spec is to allow
people to use TIFF mechanisms for adding image descriptions, put
multiple images in a single file, etc; not to tweak the original
standard.

	/F

