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Date: Thu, 10 Feb 2011 11:49:03 -0500
From: Frank Warmerdam <warmerdam@pobox.com>
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Subject: Re: [Tiff] ImageDepth tag
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On 11-02-10 11:33 AM, John Evans wrote:
> Hello, I was wondering what people's experiences are with the ImageDepth tag.
> There are a few mentions of it on this mailing list if one goes back far
> enough, but every TIFF I've seen so far (that has actually had the ImageDepth
> tag set) has had ImageDepth trivially set to 1, such as "cramps-tile.tif".
> Every TIFF except for one, that is.  That particular TIFF was pretty simple
> otherwise, photometric interpretation of MINISBLACK, SamplesPerPixel = 1,
> ImageDepth = 16.
>
> I can see how the ImageDepth tag could be useful, i.e. just one IFD with
> thousands of slices vs. thousands of IFDs each with just one slice.  And I
> can create TIFFs with with ImageDepth>  1 in other photometric
> interpretations, such as RGB and YCbCr...  but do people ever actually run
> into such beasts?

John,

I have not encountered TIFF files with non-trivial image depth values.  I
doubt there is much client software ready for them.  I'm not even convinced
that libtiff handles them well.

In *theory* I can see some utility for ImageDepth, but in practice I
would prefer to just avoid promoting it's use.

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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