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List:       imagemagick-user
Subject:    Re: [magick-users] Writing Jpeg Files
From:       Glenn Randers-Pehrson <glennrp () comcast ! net>
Date:       2002-02-28 20:27:35
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At 07:00 AM 2/28/02 -0500, I wrote:
>
>The only option available through ImageMagick is "quality" which sets
>the DCT coefficients and sets the chroma downsampling to 2x2 (quality <= 75)
>or to 1x1 (quality > 75).

Oops, that was the behaviour of 5.4.2 in December.  Now the choice of
2x2 or 1x1 chroma sampling depends on quality mod 10 > 5.  Interestingly,
this means that quality 99 will produce the best possible image, while
quality 100 will use 2x2 chroma sampling and won't be quite as good.

I'll update the man pages shortly to reflect this change.

Hmmm.
quality 70 2x2
quality 71 2x2
quality 72 2x2
quality 73 2x2
quality 74 2x2
quality 75 2x2
quality 76 1x1
quality 77 1x1
quality 78 1x1
quality 79 1x1
quality 80 2x2

I don't like that discontinuous and asymmetric behaviour very much and
would have preferred the selection to be made based on even or odd quality
values (i.e., quality mod 2 > 0).

Glenn
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