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From: Frank Warmerdam <warmerdam@pobox.com>
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To: "Adell, Albert" <aadell@icc.es>
Cc: "'tiff@remotesensing.org'" <tiff@remotesensing.org>
Subject: Re: [Tiff] Tiff JPEG compression quality factor
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Date: Fri, 28 May 2004 08:18:35 -0400
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Adell, Albert wrote:
> Hi,
> 
> I'm using the libtiff v3.6.1 and I can save a tiff file with Jpeg 
> compression and quality factor 80, but when i
> try to open it, the jpeg quality factor pseudotag has a value of 75. I 
> guess I am doing something wrong,
> because I assume that I can read the Jpeg quality factor written in 
> advance. Is that correct?

Albert,

Not that I am too knowledgable about this particular area, but my understanding
is that the quality "pseudotag" is not really saved with the data.  It is just
used to drive the compressor.  So, when you read a TIFF the value isn't derived
from the file, but just set to an initial default value (75).

In short, I don't think you can read the quality factor from an existing image.

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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