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Date: Thu, 4 Jul 2002 12:01:03 -0400
To: tiff <tiff@olympiakos.com>
From: Jon Saxton <spam.free@verizon.net>
Reply-To: Jon Saxton <js@triton.vg>
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References: <B937CE9D.BF6C%bruno_ledoux@binuscan.com> <20020703132702.GFFF27345.out018.verizon.net@thalassa> 
	<303.1025759630@sss.pgh.pa.us>
Subject: Re: Photometric interpretation for grey-scale JPEG
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** Reply to message from Tom Lane <tgl@sss.pgh.pa.us> on Thu, 04 Jul 2002
01:13:50 -0400

> Jon Saxton <spam.free@verizon.net> writes:
> > Is this correct?  If so, then should 6 be an acceptable PI for grey
> > JPEG-in-TIFF?
> 
> Absolutely NOT, imho.  1 (MINISBLACK) is correct for grayscale JPEGs.
> 
> The fact that you came across some cluelessly encoded TIFFs is not
> grounds for breaking such basic assumptions as that
> PhotometricInterpretation has something to do with the colorspace of
> the stored data.
> 
> The only reason TTN#2 doesn't spell this out in so many words is that
> it never occurred to me that anyone might think otherwise.
> 
> 			regards, tom lane
> 			organizer, Independent JPEG Group



Ouch!  I guess I have been told.  But that was the point of asking anyway.

Now, I have a follow-on question.  How is it that PhotometricInterpretation has
nothing to do with the colour space of the stored data?  In the section headed
"What data is being compressed?", TTN#2 says:

> ...  Therefore, if color conversion or downsampling are used,
> they must be reflected in the regular TIFF fields; these steps
> are not considered to be implicit in the JPEG compression tag
> value.  PhotometricInterpretation and related fields shall
> describe the color space actually stored in the file.

What part of the last sentence don't I understand?

--
Jon Saxton <js@triton.vg> Software developer for UNIX, OS/2 and Windows
U.S. agent for Triton Technologies International Ltd
http://www.triton.vg/


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