----- Original Message -----
To: "Requests for help with GraphicsMagick" <graphicsmagick-help@...>
Sent: Thursday, June 4, 2009 9:25:36 PM GMT -05:00 US/Canada Eastern
Subject: Re: [GM-help] Resize Quality
I believe IM preserves the quality of the input file if it was
a JPEG. I'm pretty sure I wrote the code to do that, but since
the source code control history of IM has been reset at least
twice since then I can't prove it.
The ChangeLog has also been restarted but I found an old
one containing this:
2003-12-22 Glenn Randers-Pehrson <glennrp@...>
* Added JPEG Quality, JPEG Colorspace, and JPEG Sampling factors to
the "identify -verbose" report. Added "-define jpeg:preserve-settings"
flag. If this is set, and the input and output formats are both JPEG,
the input quality is used to compress the output file. Also, if the
colorspace was not changed, the same sampling factors are used for
I don't know when jpeg:preserve-settings became the default behavior.
Also there is this, in the GM ChangeLog:
2003-12-16 Glenn Randers-Pehrson <randeg@...>
* coders/jpeg.c: Changed stored jpeg quality attribute from
[jpeg-quality] to JPEG-Quality. Added attributes JPEG-Colorspace
and JPEG-Sampling-factors. Added code to save and restore
these attributes when "-define JPEG:preserve-settings=yes" is
present in the comandline. Quality is restored if the input
was a JPEG and the quality was preserved. Sampling factors
are restored if the input was a JPEG, sampling factors were
preserved, and the colorspace for the output file is the same
as that of the input file.
Glenn (a.k.a. randeg)