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List:       imagemagick-user
Subject:    Re: [magick-users] jpg quality question with imagemagick and Gimp
From:       Mikolaj Machowski <mikmach () wp ! pl>
Date:       2010-09-14 17:52:55
Message-ID: 201009141952.55543.mikmach () wp ! pl
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On Tuesday 14 September 2010 15:59:31 Bob Meetin wrote:
 
> Not knowing how the compression works, what I really find curious is
> that when using -strip and a quality around 80% or above, the size is
> about the same size or larger than -strip alone. To me it would make
> sense that the following 2 commands produce the same result:
> 
> convert jensen.jpg -resize 600 -strip jensen-s600-strip-q100.jpg  (by
> ignoring quality isn't 100% assumed?)

No. Default quality is somewhat strange. From options page:

The default is to use the estimate quality of your input image otherwise 92.

Few years ago it was 75. I suppose change was introduced partially because IM 
doesn't support lossless basic operations and increase in default quality 
should counter negative effects of repeated rotation, flips, etc.

To improve quality of resize use "-sampling-factor 1x1". It will slightly 
increase image size but significantly increase look of edges in output jpg.

m.
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