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From: "Joris" <joris.at.lebbeke@skynet.be>
To: "Chris Cox" <ccox@adobe.com>, "Frank Warmerdam" <warmerdam@pobox.com>,
        "TIFF mailing list" <tiff@lists.maptools.org>
References: <45AFD224.70304@pobox.com>
	<3B96007137B4CE4E85114278E640DC33F7F749@namail3.corp.adobe.com>
Subject: Re: [Tiff] tif_getimage - using colormap even if
	photometricinterpwrong
Date: Thu, 18 Jan 2007 21:47:02 +0100
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Status:   

Chris, Frank,

Chris Cox wrote:
> Bottom line: I think the change would cause more problems than it
> would solve.
> It might solve the specific case they are describing (sounds like
> mapping data), but would likely create more problems for the larger
> TIFF user community.

I agree. This would yet again be a step away from actual TIFF. In actual
TIFF, tags that don't matter, are ignored, and that includes the
Colormap tag for Photometric MINISBLACK like it includes the T4Options
tag for Compression JPEG and the Subsampling tags for Photometric RGB.

I would recommend to solve this on the caller level. The customer with
this particular problem can use TIFFReadEncodedXxx, read the actual tag
value of Colormap (which might not currently be support without changes,
but could rightly be considered useful in a general tag access interface
regardless of image interpretation), and apply the Colormap next any way
he sees fit for his purpose.

The main thing is, you can rightly make the codec behave robust on wrong
images. But it is not right to make it behave wrong on whatever image.
That creates more problems further down the road, then it solves. Taking
a Colormap into account when Photometric is MINISBLACK is just that, it
is just wrong.


Best regards,

Joris Van Damme
info@awaresystems.be
http://www.awaresystems.be/
Download your free TIFF tag viewer for windows here:
http://www.awaresystems.be/imaging/tiff/astifftagviewer.html

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