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From: Frank Warmerdam <warmerdam@pobox.com>
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To: Joris <joris.at.lebbeke@skynet.be>
Cc: Tiff mailing list <tiff@remotesensing.org>
Subject: Re: [Tiff] How to convert MINISBLACK to PHOTOMETRIC_RGB
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Date: Fri, 23 Jan 2004 13:55:16 -0500
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Joris wrote:
> Frank Warmerdam wrote:
> 
>>"sample" == "band" == "channel" == "component" == ?
> 
> 
> Thanks Frank. Now I know I finally did understand it correctly. Am I also
> correct in thinking that the only proper way ignorant software (as in
> software that doesn't know about how the image came about or what it is
> intended to contain) can correctly interpret this 3-channel image as a
> grayscale image with 2 extra channels that have no specified
> application/meaning? If ignorant software were to have to render this image,
> the correct thing to do is to render the first channel as grayscale, and
> discard the others as far as rendering is concerned, is that right? I
> realize this may also be trivial questions, but this thread is very
> confusing.

Joris,

I am by no means an authority on the TIFF specification.  My interpretation
of the file in question is that a sensible application should render the
first band in greyscale and ignore the 2nd and 3rd since they are extra samples
with no meaning attached.  Without the ExtraSamples tag, I think an application
should assume the file contains 3 greyscale bands which might be drawn in any
number of ways.  One way would be to draw 1 band, and give the user the ability
to flip through to see the 2nd and 3rd.  Another would be to just treat them
as RGB (as many multispetral imaging packages will do with the first 3 bands
of multispectral data).

A viewing application that only showed the first band as greyscale with no
options to inspect the others would be acceptable and reasonable, but that
viewer would have little utility in the rather small work of multispectral
image processing (IMHO).

Best regards,

-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam@pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent


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