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Date: Tue, 13 Jan 2009 17:11:23 -0500
From: Frank Warmerdam <warmerdam@pobox.com>
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To: Nick <myopicwatchmaker@gmail.com>
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Cc: TIFF <tiff@lists.maptools.org>
Subject: Re: [Tiff] Libtiff compression ratios
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Nick wrote:
> Setting TIFFTAG_PREDICTOR to PREDICTOR_HORIZONTAL worked beautifully.  
> With the predictor running, libtiff's compression ratios reach parity 
> with Photoshop.
> 
> Increasing the deflate compression ratio to its maximum via 
> TIFFTAG_ZIPQUALITY had only marginal effects on compression (a 2% 
> improvement) while tripling the computation time required.
> 
> I appreciate the advice!  Perhaps PREDICTOR_HORIZONTAL might make a good 
> default value for the libtiff predictor tag?

Nick,

A case could be made for it being the default, though there are types of
images that it would perform poorly or at least with no improvement, for.

I am however not inclined to change stuff like this without careful
consideration and the impacts are not too clear to me.

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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