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From: "Joris Van Damme \(AWare Systems\)" <info@awaresystems.be>
To: "Morgenstern, James" <JMorgenstern@hpti.com>, <tiff@lists.maptools.org>
References: <5045A4D718CAB644BA24979206486B6006B9D804@hptimail03.HPTI.COM>
Date: Tue, 11 May 2010 09:29:37 +0200
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Subject: Re: [Tiff] two channel data stored as real
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Errors-To: tiff-bounces@lists.maptools.org

James,

> I have two channel image data that I want to store as real.  I have done
> the straightforward thing and set samples per pixel=2,
> SAMPLEFORMAT_IEEEFP, PLANARCONFIG_CONTIG.  The tiff readers I am using
> complain about it being a bad file.  So is the problem the tiff readers?
> Or do I not understand all there is to making two channel tiff files?

I don't think I agree with previous comments about 'picture oriented tiff 
viewers'. It's not the viewers that are picture oriented, the actual fact is 
that tiff itself is an image file format. That said, it is extremely 
suitable for storing a lot of additional info, in addition to the image that 
is.

So the first thing you need to consider, is what part of your data makes 
most sense as an image, to anyone who doesn't have additional knowledge 
about how to interpret your additional data. Depending on your exact data, 
it may be that the first channel might make most sense when interpreted as 
grayscale whilst the second channel is totally unsuitable for visual 
representation, or it might be that your data is best visualized as two 
channels out of a three-channel colorspace, or grayscale with alpha, or 
whatever. When you've dediced, you'll know how you want to store.

That way you'll have a legit tiff, and proper tiff usage. It doesn't yet 
imply that your files will be viewable by most main-stream viewers. For 
example, if you decide the first channel is best visualized as grayscale and 
the second channel is merely extra data without visual meaning, you'll find 
most viewers based on libtiff will incorrectly interpret the second channel 
as badly tagged alpha even if you properly tag it as unspecified. In 
addition to all that, you may find that most viewers are unable to deal with 
the floating point sampleformat. Not much you can do about that, this part 
is not your mistake to fix.


Best regards,

Joris

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